• Deliverability platforms [jump to section]
• Quick check tools [jump to section]
• Testing tools [jump to section]
• Monitoring tools [jump to section]
• Optimization tools [jump to section]

Disclaimer: Every tool on this list has been tried and tested by our deliverability experts, so you can expect a 100% unbiased list and reviews. You can also check our guide on how to improve deliverability yourself, to understand the main principles before picking a tool!

Best email deliverability tools: a snapshot

Click on a deliverability tool to jump ahead to the detailed review.

• Mailtrap Email Delivery Platform is the best for product companies with large sending volumes who are looking for high deliverability and industry-best analytics. 
• Postmark is for developer teams who want a reliable email API and SMTP server for sending transactional and bulk emails. 
• Email Warmup for SMBs and enterprises that want to improve their deliverability by warming up their emails.
• Mailgun is for developer teams who want to send emails or test their inbox placement, validate their lists, and preview their HTML emails in one place.
• Smartlead is for teams that are looking for unlimited mailbox support, automated warmup, and tools to maintain solid email reputation.
• MxToolbox is for users who are looking for a free solution for various quick deliverability checks or a high-end tool with advanced monitoring and deliverability features. 
• Sender Score is for people who just want to assess their sender reputation and email configuration for free before jumping to a paid solution.
• Barracuda is for teams who want to check if their IP has been flagged as spam by one of the most aggressive filters out there. 
• GlockApps is for users who need a full-stack tool for testing deliverability, email placement, and security, and can spend an extra few bucks on it.
• SendForensics is for teams who need an all-in-one deliverability platform that provides scoring for email configuration, authentication, and inbox placement.
• ZeroBounce is for people who need a full set of diagnostic tools and deliverability consulting services. 
• Google Postmaster Tools is for teams who want to analyze the performance of emails they send to Gmail users.
• Microsoft SNDS is for teams who need insight into emails they send to Outlook and Hotmail users.
• Yahoo Sender Hub is for teams who want to see how their Yahoo emails are performing.
• Everest by Validity is for heavy-duty users who need various dashboards to track their deliverability in great depth.
• InboxAlly is for people who need to improve their reputation with the most popular mailbox providers.
• TrulyInbox is for users who need to warm up their domains and improve their email deliverability and placement.

And for your convenience, here’s a table with a brief overview of each deliverability tool:

*Prices are relevant at the time of writing. I’ve added them in case you need to scale email sending volume and upgrade to a paid plan.

Best email deliverability platforms

Features such as automation, workflows, editors, segmentation, don’t matter unless your emails land in inboxes. So, instead of listing platforms with shiny features, I decided to focus on email deliverability. 

A platform with deliverability features should help you build and maintain a good domain reputation, send your emails, and analyze their performance. Ideally, it should also have testing functionalities to check your spam score, authentication protocols, and sender reputation. In other words, it should provide complete control over your email infrastructure. 

Best email deliverability platform: Mailtrap

G2: 4.8 🌟 Capterra: 4.8 🌟

Mailtrap Email Delivery Platform is designed for product companies with high sending volumes. It’s a perfect choice for companies focused on high email deliverability, in-depth analytics, and growth-focused features.

Mailtrap email deliverability features:

• High inboxing rates 

Mailtrap has high inboxing rates by design, meaning your emails will land in primary inboxes regardless of the plan you choose. For example, here’s how it performed with the free plan on our tests:

Now, just imagine the deliverability rates you can reach with dedicated IPs, auto warm up, throttling, and other deliverability features. 

• In-depth analytics

One of Mailtrap’s selling points is its analytics, which include helicopter view dashboards and drill-down reports. Through this dashboard, you can see your deliverability rate, unique open rate, unsubscribes, spam complaints, bounce rate, how your emails perform with various Mailbox Providers, and more.

• Separate bulk stream

For its high-volume email senders, Mailtrap offers a dedicated bulk stream. With its bulk-aware email API, you can send your marketing emails on top of transactional while your deliverability stays the same, all without any additional costs.

Additionally, you can use Mailtrap’s free checkers to make sure your emails are authenticated with SPF, DKIM, and DMARC or to see if your IP or domain are on blocklists. 

• Deliverability experts

Lastly, you can schedule a free consultation with one of Mailtrap’s deliverability experts, who will tell you how to optimize your sender configuration for the best possible results. We also offer tracking our customers’ Google Postmaster dashboards, so when something is off, we immediately notice them and suggest the needed fixes. 

Pricing

Mailtrap has a variety of plans you can choose from, but most importantly, you get a lot of important deliverability features by default for all plans. Check them out:

For more details, please consult the official Mailtrap pricing page.

Customer experience

Whether we’re talking about Trustpilot, Reddit or Twitter, I’m always happy to see that Mailtrap gets a lot of love on these platforms:

Postmark

G2: 4.6 🌟 Capterra: 4.9 🌟

Postmark is an email service provider that offers a reliable email API and SMTP for transactional messages. It’s a good choice for developer teams who want to send both transactional and bulk emails.

Postmark email deliverability features:

• Stable email infrastructure

Postmark has data centers in multiple locations worldwide, ensuring geographic load balancing so you can enjoy low latency and fast sending from your application/project.

Additionally, Postmark handles IP reputation, blocklists, and all of the protocol-related bits and bobs for their customers. This way, you don’t have to worry about your configuration. Instead, you can focus on sending.

Here’s how it performed in our deliverability tests:

• Separate sending stream

Similarly to Mailtrap, Postmark offers a separate sending stream you can use for bulk emails. You can also create a specific sending stream, which can come in handy if you’re sending different types of email. 

• 45 days of full email content history

If you’re into email logs, you’ll be happy to hear that Postmark is not only super detailed but also keeps your content history for 45 days.

• Real-time notifications

Postmark offers webhooks, which you can set up to get real-time notifications for email deliveries, opens, clicks, bounces, and more. 

Pricing

Considering you also get a slider to select the number of emails you want to send and adjust the plans according to your sending needs, I have to say that Postmark has great pricing. Albeit a bit more expensive than some of its competitors out there. Here’s a table that sums it up:

For more details, please consult the official Postmark pricing page. 

Customer experience

When it comes to customer experience, for whatever reasons, Postmark isn’t seeing much love on TrustPilot. However, when I went to Reddit or X, I’ve seen a lot of positive remarks like this one:

EmailWarmup

EmailWarmup is a standalone deliverability solution that combines powerful email deliverability tools into an intelligent, intuitive, and easy-to-use dashboard. It’s designed for SMBs and enterprises that operate across a range of industries: from legal, SaaS, e-commerce, healthcare, agencies, and FinTech. 

EmailWarmup studies your actual campaigns and sequences in real time and mirrors them perfectly. That way, your email warmup matches your sending style, looks natural, and is hyper-personalized, helping you reach inboxing rates as high as 98% on Pro accounts. The best part is that they back their claim with a full refund guarantee.

EmailWarmup email deliverability features

• Personalized, automated email warmup 

EmailWarmup uses AI engines powered by Claude Opus 4.1 style-guides and GPT-5, supervised by expert copywriters who understand human communication patterns, and prompt engineers who know how to guide these LLMs using NLP. 

• Free deliverability testing

Other platforms charge you $25-85 monthly for basic testing, while EmailWarmup.com gives you unlimited tests for free (forever). 

The testing network covers over 50 mailbox providers (including regional ones), and you get a comprehensive breakdown of where your emails are most likely to land. And, you can take an email deliverability test without having to worry about credit limits or surprise bills.

• Email spam checker 

You can install Email Warmup’s email spam checker browser extension in your Gmail and Outlook with one click. Once set up, you can see your deliverability rate and the percentage going to spam in real-time.

• Email deliverability consultants

EmailWarmup gives you access to a free email deliverability consultant, assigned to your account, who diagnoses and resolves any potential issues. Note that this consultation is free for all users. 

Moreover, their experts handle the technical work for you (e.g., SPF, DKIM, DMARC setup, blacklist removal, advanced segmentation strategies, etc.), working as an extension to your team. 

Pricing

If you don’t count the free tier, Email Warmup has only one plan, which gives you access to all of the platform’s features. Check it out:

Mailgun

G2: 4.2 🌟 Capterra: 4.3 🌟

Mailgun is a transactional email API and SMTP service for developers that offers a standalone Optimize suite, a set of features dedicated to improving your deliverability.

Now, I must note that Optimize is a standalone suite, so you pay for it separately. The good thing here is that you can use it in combination with any other ESP; it doesn’t have to be Mailgun specifically.

However, if you want to use Mailgun, you might be interested in how it fared in our deliverability test:

Mailgun email deliverability features:

• Mailgun Optimize

With Mailgun Optimize, you can see in which inbox folder your emails land exactly, whether it’s spam, promotions, socials, or the main inbox. 

Additionally, Mailgun included various different mailbox providers in its seed list, which is a big plus since not all mailboxes are equal.

You can also upload your email list and validate it or embed Mailgun’s API in your signup page or form to verify contacts automatically when you collect them. Or integrate it with your preferred CRM.

• Fast delivery at high volumes

Mailgun promises fast delivery at high volumes because of its Rapid Fire Delivery SLA, available on high-tier plans. Essentially, it’s SLA-backed email delivery with infrastructure capable of up to 15,000,000 emails per hour. While it is certainly achievable, it depends on your pricing plan, configuration, and domain reputation.

Also, Mailgun webhook API provides data about delivery events such as accepted, delivered, clicks, spam complaints, unsubscribes, and permanent or temporary failures. And you can configure the webhooks on a domain level. 

• Mailgun Inspect

Mailgun offers another suite of tools for building emails called Mailgun Inspect. You can use it to test email accessibility, image rendering, and email design components like buttons, links, CTAs, etc. 

And the better your emails, the more chances you have of landing in inboxes.

Pricing

Mailgun Optimize offers two different pricing tiers, and you also get one month for free, regardless of which one you choose. Here’s what you get:

And if you want to use Mailgun as your ESP, it has a similar pricing model to Postmark. Meaning, it’s got several tiers with a slider that lets you choose how many emails you want to send per month. Check it out:

For more details, please consult the official Mailgun pricing page.

Customer experience

From what I’ve found, Mailgun users are mostly satisfied with how it delivers their emails. For example:

Smartlead

G2: 4.6 🌟 Capterra: 4.3 🌟

When evaluating the best email deliverability platforms, feature lists only matter if your emails truly hit the inbox. That’s why Smartlead is designed as a deliverability-first email automation platform. 

All of its features revolve around helping you land in primary inboxes and maintain a flawless sender reputation, whether you’re sending hundreds or hundreds of thousands of emails.

Smartlead email deliverability features:

Smartlead offers unlimited mailbox support and automated warmup for each sender: it “learns” and simulates genuine human sending to build reputation across Gmail, Outlook, and custom ESPs.

You can also use unique IP servers, dynamic IP rotation, and automatic sender matching to optimize deliverability at scale, not just for one-off campaigns.

• Inbox Placement Testing & Spam Insights

“SmartDelivery” proactively tests where your emails land (e.g., inbox, promotions, spam, etc.) with real-time reports across major mail providers before launching your campaigns.

Built-in spam and readability checkers flag problematic content and provide actionable fixes, allowing you to optimize before sending.

Here’s an example report of inbox placement rating with Smartlead’s free plan:

• Comprehensive Authentication & Blacklist Checks

Automated SPF, DKIM, and DMARC validation ensures authenticated sending and greater trust with mail servers.

Blacklist monitoring and verification help you spot issues wherever they arise, even when you send at volume.

• Deliverability Analytics

With Smartlead, you can track open rates, click rates, reply rates, bounces, and sender reputation per campaign and mailbox. The central “Master Inbox” provides a comprehensive inbox view, letting you monitor all vital deliverability metrics in one place.

• Auto-Mailbox Rotation & Sending Limits

Smartlead distributes email volume over multiple accounts, preserving deliverability as you scale. Moreover, there are daily thresholds and send windows that prevent over-sending and help you navigate provider-specific limits.

Smartlead Pricing

Smartlead offers competitive plans including all core deliverability features, unlimited mailboxes, and a 14-day free trial (no credit card required). Plans can be customized to meet specific sending and outreach needs.

For more details, please consult the official Smartlead pricing page.

Best email deliverability check tools

Email deliverability check tools allow you to quickly assess whether the key factors of your email infrastructure (e.g., email authentication, domain, IP, etc.) are working well.

Some of the criteria I went by when demoing them include:

• Ease of use and speed of the check
• Accuracy of the checks I performed
• Comprehensiveness of the tool

MXToolbox

G2: 4.0 🌟 Capterra: 4.5 🌟  

Launched in 2004, MxToolbox is one of the oldest deliverability testing tools in the industry. It offers a variety of free tools for checking your domain health, and it’s pretty barebones. This makes MxToolbox perfect for people who want to quickly assess their DNS records, check if they’re blacklisted, analyze headers, etc.

For example, you can use MxToolbox’s deliverability tool to quickly validate your domains’ email authentication methods.

Simply send an email to ping@tools.mxtoolbox.com and you’ll get detailed SPF and DKIM information, header analysis, and blacklist reputation report.

Or, visit the SuperTool, an all-in-one solution by MxToolbox, enter your sending domain, IP address, or mail server hostname, and get a report regarding the following:

Pricing

MxToolbox also offers two paid plans for users who need something more than a quick deliverability check. The paid plans include access to multiple monitors for the top 30 blacklists, SPF flattening, email configuration analysis, and quite a bigger email message volume.

The plans are a bit more expensive, but they’re dedicated to enterprise users. Here they are:

For more details, please visit the official MxToolbox pricing page.

Sender Score 

G2: N/A Capterra: N/A

Sender Score is a free tool by Validity for people looking to quickly assess their sender reputation and email configuration health.

It’s also super straightforward to use, as all you need to do is open Sender Score in your preferred browser and enter your domain or IP address. You will then see your sending domain information, SSL and sending IP details, and a few other details.

Furthermore, SenderScore also tells you how you compare to others in the industry on the global average.

Another Sender Score feature I liked is the bounce lookup, which tells you why your messages are bouncing just by typing in the error message you get when you bounce. For example, I typed 4.1.2, a common potential issue with bounces, and I was taken to the page with the definition and possible fixes.

Barracuda Reputation Lookup

G2: N/A Capterra: N/A

Barracuda Reputation Lookup is a free tool you can use to check if your IP address is on the Barracuda blocklist, one of the most aggressive spam filters out there. The blocklist is maintained by Barracuda Networks, which flags IPs with a 95% accuracy rate.

According to Barracuda, most emails are flagged because they’re deemed as spam, contain viruses, or they’re sent from improperly configured email servers. 

To find out if your IP is on the list, go to the lookup page, enter your IP or domain, and click on ‘Check Reputation.’ If you are on Barracuda’s block list, you can use the Removal Request.

Note: For a detailed list of reasons why IPs are listed, consult the official Barracuda page. 

Best email deliverability test tools

Now, I’ll show you the best tools you can use to test your email deliverability, from constant monitoring to ongoing optimization.

While I was researching and demoing the tools here, I paid attention to:

• How well they reflect real-world email delivery
• The number of mailbox providers they cover (e.g., Gmail, Outlook, etc.)
• How detailed their analytics and reports are
• How easy to set up and use they are
• The range and the quality of features they offer
• The cost per test and overall pricing model

GlockApps

G2: 3.7 🌟 Capterra: 4.8 🌟 

GlockApps is a full-stack diagnostic tool for deliverability, email placement, and security.

One of its main features is Inbox Insight, with which you can see exactly where your emails are landing, whether it’s the primary inbox, spam folder, other tabs, or if they’re simply missing. 

Then, there is the DMARC Analyzer that provides you with weekly and monthly DMARC digests and sends you reports if something goes wrong. 

Uptime Blacklist Monitoring helps you keep your email authentication records healthy and notifies you if your IP gets blacklisted. So, if you don’t want to check your IP against blacklists manually with MxToolbox or Barracuda, you can use GlockApps to automate the process.

You can also book a 1-hour meeting with one of the GlockApps deliverability consultants. They’ll hear out your deliverability issues, diagnose them, and provide you with solutions on how to solve them.

Pricing

Below is GlockApps’ bundle plan, which includes both its spam and DMARC functionalities:

For more details, please visit the official GlockApps pricing page.

SendForensics

G2: 3.8 🌟 Capterra: 4.5 🌟

SendForensics is an all-in-one deliverability platform that provides scoring for email configuration, authentication, and inbox placement.

With SendForensics, you can monitor your domain and IP health, see if you’ve been blacklisted, see your DMARC failure rate, and more.

You also won’t have to worry about ending up on blacklists cause SendForensics allows you to set up alerts via email, Slack, or webhooks to notify you in real time in case you get blacklisted.

You can also run tests with SendForensics’ seed list to see how your emails are doing with the most popular providers like Gmail or Outlook and see if they’re going to the main inbox or spam. And when it comes to inbox placement with different providers, I have to say that SendForensics is quite thorough.

To round this tool up, you can monitor your DMARC compliance and preview your emails on the most popular clients and devices.

Pricing

SendForensics offers 4 different pricing plans, with the main difference between them being the amount of monthly DMARC reports you get and a number of domains and users. Everything else, such as spam tests, client previews, inbox placements tests, etc., you get unlimited.

For more details, please visit the official SendForensics pricing page.

ZeroBounce

G2: 4.7 🌟 Capterra: 4.7 🌟 

ZeroBounce started off as an email validation tool but eventually added a suite of email deliverability tools. Now it’s geared for people who need a full set of diagnostic tools and deliverability consulting services.

What makes ZeroBounce different from its competitors is its depth of email server analysis, which checks the following: 

• Header information
• RFC-based testing
• DNS records
• Email ports
• Authentication

Additionally, ZeroBounce also offers placement analytics, as well as email warmup to improve it.

Lastly, ZeroBounce has an email finder, which your outreach team will love. Essentially, it helps you find professional, validated email addresses based on name and domain, which can be useful for generating leads.

Pricing

ZeroBounce has separate pricing plans for validation and deliverability tools. Validation starts at $20,00 per 2,000 emails, whereas the deliverability suite has 4 different tiers based on your quantitative needs:

For more details, please visit the official ZeroBounce pricing page.

Best email deliverability monitoring tools

In this chapter, I’ll break down the free deliverability monitoring tools offered by the most popular inbox providers. 

These tools are important because they help you comply with the latest sender requirements released by the most popular mailbox providers (e.g., Google, Yahoo, Outlook, Apple.). If you don’t comply with these, your emails will be rejected, which directly impacts your deliverability.

Check out our dedicated blog articles for more details:

• Google and Yahoo Email Sender Requirements
• Outlook’s New High-Volume Sender Requirements Update

Google Postmaster Tools

G2: N/A Capterra: N/A 

Google Postmaster Tools is a tool that lets you analyze the performance of emails you send to Gmail users. More specifically, you can monitor:

• Compliance status
• Spam rate
• IP reputation
• Domain reputation
• Feedback loops (FBL)
• Email authentication
• Email encryption
• Delivery errors

To start using Google Postmaster Tools, you will need a regular Google Account or a Google Workspace account and a registered sending domain. For a step-by-step guide on setting up Postmaster, check out our dedicated article on the topic.

Moving on, the tool itself consists of several dashboards, such as the Compliance Status dashboard, which lets you see if you’re compliant with the aforementioned email sender requirements. If you see a ‘Needs work’ status, it means you’ll have to tweak your sending configuration a bit.

Then, there is the spam rate dashboard, which tells you what percentage of your emails have been reported by recipients. To comply with Google’s requirements, you need to be under 0.3%, whereas the industry standard is 0.1%.

Two other very important dashboards are the IP and domain reputation dashboards. Here, you should aim for Medium and High, or yellow and green, since everything below means that ISPs don’t think you’re a legitimate sender and don’t consider your emails trustworthy.

Microsoft SNDS

G2: N/A Capterra: N/A 

Microsoft SNDS is a tool offered by Microsoft that lets you know how your emails sent to Outlook and Hotmail users are performing. It mostly concerns:

• Email IP reputation
• IP address activity
• Spam complaints
• Spam trap hits
• Spam rate

To set up Microsoft SNDS, you need a Microsoft account, the IPV4 address of your sending server, and access to the associated domain’s reverse DNS to verify ownership.

Unlike Postmaster, Microsoft SNDS consists of only one dashboard with many columns for monitoring different things, like the Filter result, for instance. This is likely the most important column since it scores your IP address health based on how many emails you hit Outlook spam filters. 

Right next to the filter result, you’ll find the complaint rate, which shows the percentage of recipients who reported your message as spam. 

You can also see whether you hit a spam trap maintained and managed by Outlook. For example, this would be nearly impossible to detect without Microsoft SNDS.

P.S. We also have an in-depth article breaking down Microsoft SNDS and a video explaining the Outlook high-volume email sender requirements. 👀

Yahoo Sender Hub

G2: N/A Capterra: N/A 

Yahoo Sender Hub is a tool that allows you to monitor the performance of emails you send to your Yahoo contacts. Through its dashboard, you can track your:

• Domain reputation 
• Authentication status
• Spam complaint rates
• IP reputation
• Inbox placement

To use Yahoo Sender Hub, you need a Yahoo account, a verified sending domain, and proper email authentication.

Overall, Yahoo probably has the most modern dashboard out of all inbox providers, which makes sense since it’s a relatively new tool, having launched in 2024. It’s super easy to use and set up and has all the stats you need to comply with Yahoo’s requirements.

Additionally, if you’re feeling tech-savvy, it also supports advanced email technologies, such as AMP or Brand Indicators for Message Identification (BIMI). You can use these to improve your brand visibility in your recipients’ inboxes.

Best email deliverability optimization tools

Email deliverability optimization tools are designed to actively enhance your inbox placement. What I mean by this is that your goal is not only to land in the inbox but to end up in your recipients’ primary folder.

So, I evaluated the following tools based on:

• How effective they are at improving my sender reputation
• How easy to set up, integrate, and use they are
• Whether some of their functionality can be automated
• How sustainable their deliverability improvements are

Everest by Validity 

G2: 4.2 🌟 Capterra: 5.0 🌟

Everest is a platform that provides various dashboards for tracking your email deliverability. Think of it like a highly customizable cockpit for email marketing.

With Everest, you can track basic email engagement metrics, such as opens, uniques, average read time, etc. But you can also get an insight into what % of people skim your emails, what time they read them the most, from which devices, and more.

With Everest, you can track feedback loops for over 30 mailbox providers and get valuable information such as spam complaints. 

Tip: You can also integrate Everest with your Microsoft SNDS and Google Postmaster Tools accounts to monitor your reputation.

However, Everest is not only about dashboards. You can also use it to preview your designs across major devices and mailbox providers, test your subject lines and email content for spam, and see if you’ve passed authentication checks or if you’re on blocklists.

If you want to stay above the competition, Everest allows you to track competitors’ sending patterns and see what they’re doing. This way, you can determine the best performing days in your niche, adjust your email sending configuration, and ensure your messages stand out. 

Pricing

Although slightly on the more expensive side, Everest has pricing plans for businesses of all sizes:

For more details, please visit the official Everest pricing page.

InboxAlly

G2: 4.6 🌟 Capterra: 5.0 🌟

InboxAlly is a tool that teaches inbox providers to understand that emails coming from your domain are trustworthy and are wanted by your recipients. Think of it as a more advanced form of email warm up that improves both your deliverability, as well as your engagement. 

To achieve this, InboxAlly sends emails to seeded inboxes, automatically opens them and clicks links. Additionally, InboxAlly also has the option to reply to some of the emails, mark them as ‘Not spam’ if they end up in spam, or if they end up in the wrong folder, like ‘Promotion’ for example, move them to the primary one. This makes inbox providers see that your email content is valuable. 

To achieve this, InboxAlly provides you with a list of seed emails you can download and add to your email-sending software. 

Then, you create a sender profile where you choose the engagement actions you want InboxAlly to take. For example, the tool can:

• Warm up your domain
• Open your seed emails
• Click on the links
• Move them to a specific folder
• Mark them as not spam (if they end up in spam)

All of this happens automatically once you send the seed emails.

After sending the emails from your email-sending service, you’ll be able to monitor their activity and inbox placement in the InboxAlly broadcast dashboard.

Oh, and one more thing, InboxAlly offers a free spam tester that doesn’t require either an account or a sign-up. You just send your usual content from your sending address to the InboxAlly audit email, and they’ll send you a free audit and deliverability report.

Pricing

InboxAlly pricing is super simple, as it mostly revolves around the amount of daily seed emails allowance. So, the more you pay, the more you can warm up your emails:

For more details, please visit the official InboxAlly pricing page.

TrulyInbox

G2: 3.1 🌟 Capterra: N/A

TrulyInbox is an email warm-up tool that improves your email deliverability and inbox placement by building positive sender reputation for major mailbox providers through gradually sending simulated human-like interactions with other users. 

The tool is pretty straightforward, as all you need to do is add your email account and provide the necessary information like in the screenshot below:

Currently, supported email service providers include:

• Gmail/Gsuite
• Office 365 (nATIV)
• Outlook.com/Hotmail.com/Live.com
• Yahoo Mail
• Zoho
• GoDaddy
• Yandex

Once you’ve added your email account, you configure your preferred warm-up settings by selecting how many emails per day you want to send, reply rate, etc.

Upon starting the process, TrulyInbox adds you to their warm-up pool and starts automatically sending emails from your mailbox to other users simulating real-life user exchanges.

The key phrase here is ‘real-life user exchanges’ because the emails look something like this:

You can also track the inbox placement of your warm-up emails, albeit the analytics are a bit minimal, but they do the job nonetheless.

Pricing

When it comes to pricing, I have to say that TrulyInbox is quite affordable and straightforward. Each plan offers a specific amount of warm-up emails and a reply-rate specific to it, which increases as the cost does. There’s also a free plan and some tech features like warm-up API:

For more information, please visit the official TrulyInbox pricing page.

Wrapping up

If you’ve made it this far, congratulations! You’re one step closer to becoming an email deliverability expert. 

One last tip to go: Don’t be afraid to mix up the tools on this list. For example, pair Google Postmaster Tools with Microsoft SNDS or use Everest to combine them both. The possibilities are endless.

Also, don’t get caught up in all the email metrics and data and forget to implement best practices. As one Reddit user would put it:

For more actionable tips and tricks, check out our blog, where we’ve paved the way for you with articles such as:

• What Is Email Feedback Loop and Why Is It Important?
• Email Protocols Explained: IMAP vs POP3 vs SMTP [2025] 
• Cold Email Marketing: Definition, Importance, and Guidelines
• 13 Reasons & Solutions for Why Your Emails Are Going to Spam 

Below, you’ll find proven ways to spot problems early, fix them fast, and keep your emails reaching the inbox.

Email deliverability issues: a snapshot

Before we get deeper, here’s your emergency reference guide. Print this out and stick it on your wall:

These quick actions prevent further damage to your deliverability rate. But if you want a structured approach on how to fix email deliverability issues, you need to understand what’s really happening behind the errors.

How to diagnose email deliverability problems

You can’t fix what you can’t measure. Too many businesses discover deliverability issues weeks after their email campaigns start, when the damage is already spreading. Here’s my systematic approach to troubleshooting email delivery issues before they explode.

Start with the metrics that matter

Forget vanity metrics. When I’m diagnosing deliverability, I focus on five core metrics:

• Bounce rate by type and ISP: Track bounces by both bounce type and by provider. For example, your overall bounce rate might be 2%, but if Gmail is bouncing 15% of your emails, that’s a clear deliverability problem. I segment bounces by provider to catch patterns: a sudden spike in Yahoo bounces, for instance, tells me that Yahoo is signaling something’s wrong.
• Provider-specific open rates: Overall open rates have become less reliable (thanks to Apple’s Mail Privacy Protection), but comparing open rates by email provider reveals where your emails are landing. If Gmail’s open rate drops by 50% while others (Outlook, Yahoo, etc.) remain steady, it’s a clear sign your Gmail sender reputation took a hit and more of your messages are likely going to spam.
• Spam complaint rates in context: Look beyond your aggregate spam complaint percentage; consider where any complaints are coming from. One complaint per 1,000 emails is usually fine, but if those complaints all come from a specific email campaign or list segment, you’ve pinpointed a problem. I track complaints by campaign, list source, and content type to find specific pockets that need attention.
• Engagement velocity: Measure how quickly people open or click your email after it’s delivered. If emails sit unopened for hours, mailbox providers take it as a sign that recipients don’t value those messages. I monitor what percentage of opens (and clicks) happen within 1 hour, 6 hours, and 24 hours of sending.
• Reply rates for key messages: A reply is the gold standard of email engagement. When someone replies to your email, it’s the strongest positive signal you can get. I closely watch reply rates on especially important emails like welcome messages and transactional emails, if those reply rates drop, it’s a red flag that often predicts future spam filtering issues.

Decode your server logs

Your SMTP server logs contain answers to many deliverability mysteries, if you know how to read them. Here’s what I look for:

• “550 5.7.1” — blocked for policy reasons (usually a sender reputation issue).
• “421 4.7.0” — you’re being rate-limited (the recipient server is telling you to slow down).
• “550 5.1.1” — invalid address (the recipient email doesn’t exist).
• “554 5.7.5” — spam filter rejection (triggered by spammy content in your message).

Temporary failures (4xx codes) that keep happening will eventually turn into permanent blocks unless your suppression and retry automation catches them. If I see the same address getting a 421 error repeatedly, I know we’re one step away from a full block.

I also watch for timing patterns in the SMTP exchange: 

• Delays between connection and acceptance indicate greylisting by the receiving mail server (the server is deliberately delaying unknown senders). 
• Immediate rejection as soon as you connect? That’s usually a blocklist hit. 
• Inconsistent behavior between successive tries? Your sender reputation is borderline, and the ISP can’t decide whether to trust you.

Master the ISP feedback tools

Google Postmaster Tools is non-negotiable. Track your email domain reputation trends (High → Medium is an early warning), compare IP reputation versus domain reputation to isolate infrastructure vs. list/content issues, watch authentication success rate (SPF, DKIM, DMARC should be 100%), and check encryption rate (aim for 100%; lower suggests an outdated setup). 

For Microsoft, use SNDS (Smart Network Data Services) for Outlook/Hotmail to spot spam trap hits, complaint rates, and filtering/throttling, and pair it with JMRP (Junk Mail Reporting Program) to receive user junk reports.

Test emails before you send

Always pre-flight. First run the email messages through Email Sandbox for a SpamAssassin score, SPF/DKIM/DMARC alignment, and any missing-header or malformed-HTML issues. 

Then send to a seed list across Gmail, Outlook, Yahoo, Apple, and corporate domain names; check folder placement (Primary/Spam/Promotions tab), delivery time, whether images load by default, and the visibility/function of the unsubscribe link. 

If seeds reveal problems (e.g., Gmail sends it to Spam or Yahoo shows delays), halt and fix before the full send.

Run the technical health checks

• SPF records (Sender Policy Framework): Use Mailtrap’s SPF checker; stay under the 10 DNS lookup limit; include all sending services; never use +all; avoid duplicate records. (Gmail and Yahoo require valid SPF for bulk email senders.)
• DKIM signatures (DomainKeys Identified Mail): Validate with a DKIM validator; use keys ≥ 1024-bit (2048-bit preferred); make sure the DNS selector matches your ESP; confirm recent key rotations have propagated; avoid conflicting selectors across systems.
• DMARC policies: Implement DMARC (start with p=none to monitor). Ensure alignment between your From domain and SPF/DKIM. Monitor aggregate reports (RUA) and cover subdomains in your policy. DMARC protects against spoofing and is increasingly required by Yahoo, Gmail, and Microsoft. Roll it out in phases: p=none (monitor) → p=quarantine (soft enforcement) → p=reject (full enforcement) once legitimate mail consistently passes.

Check blocklists before they check you

Even if everything else looks fine, you should check if your sending IP or domain has landed on any blocklists. I run a blocklist scan every week, and believe me: catching a listing early can save you days of damage. Mailtrap’s blacklist checker (or a similar tool) covers the major lists. Here’s how I interpret results from a few of the big ones:

• Spamhaus: If you’re listed here, it means you have serious problems (often spam traps in your list or a compromised server). It’s a high-severity red flag.
• Barracuda: Often triggered by a poor sender reputation or spammy content issues.
• UCEPROTECT: This one can be overly aggressive, but a listing usually points to high volume of emails or complaint rate problems.
• SpamCop: Typically means user spam complaints or spam trap hits got you flagged.

If you do find yourself on a blocklist, don’t panic and immediately request removal. First, identify and fix the root cause of the listing. (Prematurely asking for delisting without addressing the problem can get you denied and make it harder to get off the list later.)

Once the underlying issue is resolved, you can request delisting with a clear explanation of what you fixed.

Email deliverability issues: detailed look and solutions

Now let’s get to the bottom of specific deliverability problems and how to solve them.

Technical setup

In my experience, most deliverability crises trace back to a technical misconfiguration that stayed invisible, until suddenly it caused an issue.

Email authentication issues

Email authentication is your proof of identity in the email world. Without proper SPF, DKIM, and DMARC, you’re essentially sending emails without ID.

SPF problems are common and create instant trust issues. The top failure is exceeding the 10 DNS lookup limit after piling on services. When SPF fails, receivers treat the mail as spoofed. 

How to fix it? audit all senders (ESPs, CRMs, support tools, etc.), consolidate where possible, use include mechanisms efficiently, consider SPF flattening for complex setups, and test after every change, the smallest typo can break the record.

DKIM adds a cryptographic signature, but failures are often intermittent. Causes include one-character DNS typos, rotating keys without updating the DNS record, or multiple systems double-signing with conflicting selectors. 

To address this, trace every system that signs, confirm each public key matches its private key, test with multiple samples (not just one), and monitor pass rates in Google Postmaster Tools to verify consistency.

Many domains still lack DMARC, forfeiting visibility and protection. DMARC reports reveal who’s sending mail as your domain, and a proper policy gives receivers confidence to deliver your messages. (Yahoo and Gmail now require DMARC for high-volume senders, and Microsoft is moving that way too.) 

Implement DMARC in phases: start with p=none to gather data, advance to p=quarantine as issues are resolved, and finish at p=reject once legitimate mail consistently passes. DMARC (when aligned with SPF/DKIM) protects against spoofing and keeps you in good standing with mailbox providers.

DNS/PTR records

Your DNS setup can signal legitimacy or shadiness to receiving servers. Small details here have massive impacts:

• PTR records (reverse DNS): Ensure every sending IP has a valid PTR record that maps back to a domain you control (ideally one aligned with your sending domain). Avoid generic ISP-provided rDNS. Missing or mismatched PTR records are a common reason for receiving servers to reject your emails.
• MX records: Even if you don’t plan to receive mail at a particular sending domain, publish an MX record for it that at least accepts or properly rejects incoming messages. Domains that can’t receive mail at all look like one-way spam operations and get extra scrutiny from receivers.

TLS encryption

Always send over TLS (at least version 1.2, and 1.3 preferred) with valid, up-to-date certificates on all sending hosts. Inconsistent or missing TLS can trigger warnings in Gmail and lead to outright rejections at stricter organizations, hurting both your security and your deliverability. 

Make sure every mail server you use offers TLS and that your sending software is configured to use it.

If you’re unsure how your provider measures up, check out our SMTP providers security comparison, there we broke down which services fully support encrypted delivery and how they handle authentication.

Sender reputation

Sender reputation (or sender score) builds slowly through good behavior and can be wrecked almost overnight by mistakes. Unlike a credit score, it won’t heal on its own, you need deliberate action to improve it once damaged.

Domain reputation

Domain reputation reflects how mailbox providers judge your sending domain across all IPs and services. When it goes down, everything suffers, even transactional messages (e.g. password resets, invoices, shipping notifications) can be filtered out. 

Domain reputation is damaged quickly and heals slowly. Key drivers include your historical sending patterns and volumes, spam complaint rates, positive engagement rates (opens, clicks, replies), bounce rates, spam trap hits, and consistent authentication results.

Recovery requires systematic improvement:

• Week 1 – Stop digging: Pause all non-essential sends. Deliver only critical transactional emails (password resets, order confirmations, etc.). During this time, audit your authentication, remove any clearly unengaged or bad addresses, and double-down on list hygiene to prevent further damage.
• Weeks 2-4 – Rebuild trust: Send only to your most recently engaged users (e.g. those who opened or clicked in the last 30 days), and send at a much lower volume than normal. Provide clear value in these emails. Monitor engagement rates and complaint rates like a hawk and address any issues immediately.
• Weeks 5-8 – Gradual expansion: Slowly increase volume (perhaps 10-20% more each week) and start including slightly less recent segments (e.g. those engaged in last 60 days, then 90 days). Keep a close eye on each ISP’s metrics; if Gmail or Yahoo open rates dip or complaints even hint at rising, scale back and wait.
• Week 9+ – The new normal: Continue raising sending levels carefully until you’re back to your normal volume, but keep higher standards for engagement than you had originally. Maintain the rigorous list hygiene and monitoring permanently. The disciplines you followed during recovery should become your new routine to prevent backsliding.

IP reputation

The choice between using dedicated IP addresses or shared IP pools significantly affects how much control you have over this aspect of reputation.

With dedicated IPs, you have complete control but also complete responsibility for that IP’s reputation. 

The most critical phase for a dedicated IP is the warm-up period. If you rush to send high volume on a brand new IP, you’ll trigger throttling or blocks that could take weeks to resolve. 

When I warm up a new dedicated IP, I start extremely conservatively and only ramp up based on email performance:

• Days 1-3: Send about 50 emails on day 1, ~100 on day 2, ~200 on day 3, and send only to your most engaged users these first few days.
• Days 407: Double your daily volume each day (roughly 400, 800, 1,600, 3,200…) until you’re sending around 5,000/day by the end of the week (still only to highly engaged recipients).
• Week 2: Continue increasing volume by roughly 50% per day, but keep a very close watch on metrics and any ISP feedback (bounces, spam warnings).
• Week 3+: Gradually keep boosting volume as long as metrics stay healthy. Be ready to pause or slow down at the first sign of trouble (e.g. rising complaints or plummeting open rates). Adjust your warm-up speed based on how each major provider (Gmail, Outlook, Yahoo, etc.) is reacting.

Automated warm-up tools like Instantly.ai or Warmforge can help by generating real conversations between high-reputation accounts, boosting sender credibility in the background.

On shared IPs, your deliverability depends on others. Ask your Email Service Provider how they vet senders, handle spammers, and whether they can move you to a better pool or a dedicated IP if needed. Good providers actively manage their IP pools to protect reputable senders from bad neighbors.

Blocklisting

Landing on a blocklist can disrupt email delivery, but it’s a challenge you can address if caught early. One day your sends are performing normally; the next, a provider or filter may start rejecting or filtering more of your messages. 

That’s why it pays off to check blocklist status weekly. Early detection often means you can resolve the issue before it affects a significant portion of your audience.

Understanding how you got blocklisted helps prevent it from happening again. The #1 cause I see is hitting spam traps. Spam traps are addresses that look valid but exist solely to catch senders who aren’t following best practices. They end up on your list through:

• Purchased or scraped lists: These always contain spam traps. If you buy a list, assume it’s poisoned.
• Poor signup form protection: Bots or malicious actors can submit fake emails. Typos like john@gmial.com can also be spam traps if someone intentionally registered that typo.
• Old, recycled addresses: Emails that were once active but have been abandoned and later turned into spam traps.
• Lack of regular list cleaning: If you keep emailing an address that hasn’t engaged in years, it might have turned into a trap without you realizing.

Volume patterns can trigger blocklistings too. The classic “snowshoe” spamming technique, spreading a huge volume across many new IPs and domains, is a red flag. If a normally legit sender suddenly behaves that way, or if spam complaints jump sharply (e.g., 0.2% when you’re usually at 0.02%), a blocklist listing may follow fast.

How to get off a blocklist, what works:

• Identify the root cause: Read the blocklist’s notice and examine your recent sending data. “Spam trap hits” → list quality issue. “Policy violation” → authentication or sending practices issue. Check your bounces, complaints, and any recent changes (like new list sources).
• Fix it completely: Scrub your list (remove any suspicious or inactive addresses), enforce double opt-in going forward, add CAPTCHA to signup forms, optimize targeting and content relevance, and make sure unsubscribe is easy to find. In short, eliminate whatever behavior got you listed. Do not request delisting until these fixes are in place.
• Document remediation: When you request delisting, be ready to explain what went wrong and exactly what you changed to fix it. If you can, show some proof of improvement (e.g., “We’ve removed 5,000 old addresses; our hard bounce rate dropped from 5% to 0.2%”).
• Request delisting professionally: Follow the blocklist’s process, be polite and honest in your request, and avoid any tone of blame or excuses. A brief, factual explanation and assurance that the issue is resolved works best.
• Monitor after delisting: Once you’re off, consider yourself on probation. Keep your sending volumes modest for a while, stick to highly engaged recipients, and watch your delivery and engagement metrics daily. A relist can happen quickly if the root cause wasn’t fully fixed or if it comes back.

Email list

Your email list can work for you or against you. Valid, engaged, and fully consenting subscribers strengthen your ability to reach the inbox, while invalid addresses, inactive contacts, and recipients who never opted in can quietly undermine your deliverability and overall campaign performance.

Non-permission list

I can’t emphasize this enough: sending email to people who never explicitly gave you permission is not a good idea. 

There are laws like GDPR and CAN-SPAM that can land you in legal trouble (with fines potentially in the millions), but beyond legal issues, the technical consequences are immediate and severe.

When you email people without proper consent:

• Spam complaint rates will spike (even a 0.3-0.5% complaint rate is catastrophic in deliverability terms).
• Your engagement metrics will crater because people ignore or delete emails they didn’t ask for.
• ISPs quickly identify your messages as unwanted and start filtering everything to spam.
• Your domain and IP reputation tanks, and it can take months of work to recover.

Examples such as collecting a business card at an event, having someone download a whitepaper, purchasing a targeted list, or emailing past customers don’t automatically qualify as true consent for email marketing. Without explicit opt-in, these contacts are more likely to ignore or mark your emails as spam, which harms deliverability over time.

The most reliable approach is to build your list through confirmed opt-ins, ensuring recipients genuinely expect and want your messages.

High bounce rates

The bounce rate is a loud signal to mailbox providers. How you handle bounces separates professional senders from spammers and defines your list hygiene practices:

• Hard bounces are permanent delivery failures, such as “User unknown” or “Domain not found.” These addresses should be removed from your list immediately and not emailed again. Continuing to send to hard bounces signals poor list hygiene and can negatively impact deliverability.
• Soft bounces (temporary issues like “Mailbox full” or server not responding): You can retry these a few times, but then stop if the issue persists. A practical rule: if an address soft bounces on three consecutive sends over, say, 1-2 weeks, treat it as a hard bounce and suppress it.

High churn rate

A high churn rate, meaning you’re losing a lot of subscribers over time through unsubscriptions or inactivity, indicates potential problems with your list quality or email strategy. To keep your list healthy and minimize churn, practice strict list hygiene and proactive engagement management:

• Regular scrubbing: Remove or suppress subscribers who have shown no engagement (no opens, clicks, or replies) for 6 months or more.
• Pre-emptive validation: Use double opt-in and real-time email verification on sign-up to prevent typos or fake addresses (e.g. @gmial.com) from ever entering your list.
• Watch role accounts: Be cautious with addresses like admin@, info@, or other generic aliases. These recipients are less likely to engage and more likely to mark emails as spam or ignore them.
• Catch typos and traps: Implement measures in your signup forms (like “Did you mean gmail.com?” prompts) to catch common typos. Also, monitor sign-ups for known spam trap patterns and exclude those addresses.
• Engagement-based segmentation: Send less frequently (or pause sending) to users who haven’t engaged recently. You can run targeted re-engagement campaigns to try to win them back, but don’t keep mailing the truly inactive indefinitely. Keep your most engaged subscribers on your primary schedule, and slow down for the rest.
• Let go of unresponsive contacts: If re-engagement campaigns fail to reawaken a segment of your list, remove those contacts. It’s better to lose them from your list than to keep emailing people who don’t want to hear from you; that only hurts your deliverability in the long run.

Email content

Your email content directly impacts whether your messages reach the inbox. Modern spam filters don’t just look for a few “spammy” words and the number of emails. They examine everything from your subject lines and formatting to your links and images.

Low engagement

Low engagement slowly erodes deliverability: if recipients routinely ignore or delete your messages, mailbox providers assume those emails are unwanted and start filtering them to spam. Keep engagement high with three fundamentals:

• Engaging subject lines: Aim for ~50 characters and set clear expectations. Avoid clickbait, spammy buzzwords (such as the word “buzzword”), and excessive punctuation or capitalization. A/B test different styles on small subsets of your list and see what boosts open rates.
• Immediate value + clear CTA: In the email body, lead with the main benefit or reason for the email. Keep paragraphs short and the layout scannable. Emphasize key points (bold or bullet important info) and include a specific call-to-action (CTA) that stands out, so readers know exactly what to do next. 
• Meaningful personalization. Use segmentation and dynamic content to tailor emails based on behavior or preferences (e.g., different messages to frequent buyers vs. infrequent, or to users who clicked on certain content). References to recent actions (like “since you downloaded our guide last week…”) show relevance. 

Spam content

Spam filters today analyze complex patterns, and even well-meaning, legitimate marketers can accidentally trigger those filters without realizing it.

For example, here are some common content issues with email deliverability that can trigger filters:

• Formatting red flags: Emails that consist of one large image (with little or no text) are suspect: spammers often hide text in images to evade filters. Other red flags include:
  • Weird formatting like extremely small or light-colored text
  • Overly large fonts
  • Lots of red-colored text or highlighting
  • Using ALL CAPS for extended sections
  • Overusing exclamation marks and symbols.
• Suspicious content patterns: filters get wary if your email has, say, one big image with a single hyperlink and almost no text. Using URL shorteners or having multiple redirects in your links is another red flag since it can look like you’re hiding the true destination (a common phishing tactic). 
• Mismatched link text (where the hyperlink says one thing but actually goes somewhere else) also appears deceptive. And don’t forget the basics: if you omit a physical mailing address or an obvious unsubscribe link, many spam filters will penalize you immediately.
• Certain technical mistakes in email structure trigger spam filters:
  • Broken HTML code – unclosed tags or malformed elements can get flagged.
  • Missing ALT text on images: filters may assume you’re hiding text in graphics.
  • No plain-text version: many email clients (and some filters) expect a text alternative alongside the HTML version.
  • Large file size: too many images or bloated code can push the email over safe limits.
    Scripts or ActiveX: including JavaScript, Flash, or ActiveX looks malicious and gets you blocked outright.

Because of these risks, I always test my content before sending to the full list. Most of these times I use Spam Checker, which gives me a SpamAssassin score and flags exactly which rules (if any) my email might be tripping, suggests content improvements, validates that my HTML is well-formed, and checks the reputation of my links. 

I’ve found that even improving a spam score by 0.1 or 0.2 points can mean thousands more emails reach the inbox.

High unsubscribe rates

If your unsubscribe rates are high, it’s a clear sign that recipients are dissatisfied with your emails. Often this means your content or sending frequency isn’t meeting the expectations you set when they subscribed. 

To address this, make sure subscribers know exactly what they’re signing up for and how often they’ll hear from you, and then deliver on that promise.

Offer a preference center so users can choose what topics they receive and adjust email frequency rather than leaving entirely. And above all, always include a visible, no-questions-asked unsubscribe link in every email; if people can’t easily opt out, they’re more likely to hit the “Report Spam” button, which is far worse for your sending reputation.

Email sending

How you send matters just as much as what you send. Sloppy sending practices can trigger defensive measures by ISPs that are designed to stop spammers, so you need to send the right way.

Volume spikes / throttling

Avoid sudden volume spikes. Ramp up gradually: about 25% more daily each week before a big campaign, so ISPs treat the higher volume as normal. Distribute large sends over several hours, account for time zones, and use your ESP’s throttling/scheduling tools to avoid ISP rate limits.

Provider quirks matter: Gmail prioritizes domain reputation and engagement history; Outlook/Hotmail is strict on authentication alignment and throttles sudden surges; Yahoo reacts to rising spam complaints; many corporate servers block bulk patterns entirely. Match your pace to each provider’s expectations.

Sending frequency

Keep sending frequency consistent with subscriber expectations. Too often causes fatigue; too rarely leads to disengagement and deliverability issues. Adjust based on engagement; frequent sends for active subscribers, lighter touch or re-engagement for inactive ones. Be clear upfront about cadence and stick to it.

Not separated IP pools

Sending all emails: marketing newsletters, transactional receipts, account alerts, from the same IP/domain risks one stream’s problems hurting all others. Separate your sending infrastructure by use-case:

• Separate domains/subdomains: e.g., transactional.yourdomain.com for confirmations/resets, marketing.yourdomain.com for newsletters, alerts.yourdomain.com for app notifications. If marketing gets spam-foldered, it’s not what affects email deliverability for transactional messages.
• Dedicated IPs per stream: Keep transactional on one pristine IP, marketing on another, and high-risk/cold emails on a separate IP. Each IP needs its own warm-up and steady volume to maintain good reputation.
• Isolated suppression lists: Marketing opt-outs shouldn’t block account notices; newsletter bounces shouldn’t suppress valid transactional addresses.

How to keep high email deliverability

Fixing problems after they appear is expensive and slow. The most reliable way to keep emails out of spam is to prevent deliverability issues from happening in the first place. That means building processes, infrastructure, and monitoring routines that protect your sender reputation day after day.

Build quality into every process 

Stop bad data at the door. Use double opt-in, CAPTCHA on all signup forms, and real-time email validation to block typos and fakes. Set expectations for content and sending frequency at signup. Track list source quality and drop any that generate bounces or low engagement.

Authentication should be bulletproof

Treat SPF, DKIM, and DMARC as ongoing maintenance. Review monthly, audit quarterly, and re-test after any change (new domain, ESP). Monitor Google Postmaster Tools for pass rates near 100% and fix dips immediately. Keep DNS documentation, rotate DKIM keys, renew TLS certificates, and consider BIMI once everything is solid.

Monitor what matters

• Daily: Check bounce rates by type/ISP, spam complaints, engagement, delivery delays, and authentication status.
• Weekly: Review domain/IP reputation in Postmaster and Microsoft SNDS, run blocklist checks, analyze engagement by cohort.
• Monthly: Audit inbox placement rate, delivery rates, and industry news. Adjust infrastructure (e.g., warm a new IP) or processes (tighten opt-in).

Use infrastructure that supports success. Choose an Email Service Provider with real-time deliverability monitoring, automated bounce/complaint suppression, ISP feedback loop integration, and flexible IP pool management. The support team should be deliverability experts, not script readers. Quality infrastructure improves inbox placement rate and prevents crises.

Use a reliable email service provider

Your deliverability is only as strong as the platform you send from. A reliable ESP should handle the technical details that protect sender reputation and maximize inbox placement. Mailtrap does this by default:

• Authentication handled: SPF, DKIM, and DMARC records are generated, validated, and kept in sync so every message is properly authenticated.
• Isolated sending streams: transactional and bulk emails run on separate infrastructure and IPs, preventing marketing issues from spilling over into critical messages.
• Automatic suppression lists: hard bounces, spam complaints, and unsubscribes are suppressed immediately, so you don’t risk resending to invalid or uninterested addresses.
• Deliverability monitoring: weekly health reports, real-time alerts, and dashboards help you react to problems before they escalate.
• Secure and compliant: GDPR-compliant and ISO 27001 certified, with TLS encryption across all email traffic.

With this infrastructure in place, you can scale confidently, knowing your messages have the technical foundation to reach the inbox. Check out what else Mailtrap can do! 🔽

Stay ahead of industry changes

Follow ISP postmaster blogs (Google, Microsoft, Yahoo), join email industry forums, and maintain expert contacts. React early to changes like Apple MPP, Gmail/Yahoo authentication rules, Microsoft’s stricter filtering, privacy regulations (GDPR), and enforced one-click unsubscribe. Being proactive keeps you ahead while others scramble.

Email deliverability monitoring tools

You can’t manage what you don’t measure. The following are some tools and platforms I use regularly to keep tabs on deliverability and ensure everything stays on track:

Essential ISP tools

Every serious sender should take advantage of the free postmaster tools offered by the big mailbox providers:

• Google Postmaster Tools: This gives you unmatched visibility into how Gmail is treating your email. You can monitor your domain and IP reputation scores, see your spam rate as Gmail measures it, check your authentication success rate, and even verify that you’re meeting Gmail’s TLS encryption requirements. I log into Postmaster Tools at least weekly (daily if I’m troubleshooting an issue). Often those reputation graphs will show a downward trend or problem before it manifests as a significant delivery issue.
• Microsoft SNDS & JMRP: SNDS (Smart Network Data Services) is Outlook/Hotmail’s equivalent for monitoring your sending IPs. It shows data like how many Microsoft spam traps you hit, your complaint rates, and whether you’re being throttled or filtered by Microsoft. If you use dedicated IPs, SNDS is crucial. I also use Microsoft’s Junk Mail Reporting Program (JMRP), which sends me feedback loop reports whenever a user on Outlook/Hotmail marks one of my emails as junk. Between SNDS and JMRP, I can get a pretty full picture of how Microsoft is treating my emails.
• Yahoo/AOL Feedback Loop works the same way, sending alerts when users mark messages as spam. I recommend registering for every ISP feedback loop you qualify for, including Comcast, Cox, and others. More complaint data means faster remediation.

When I want an external perspective, I’ll also check tools like Cisco Talos Intelligence or SenderScore.org to see how my IP/domain is viewed across the broader email ecosystem, not just by Gmail or Microsoft.

Deliverability test and validation platforms

Before sending any major campaign, I use an email testing platform to check email deliverability issues before they happen. Email Sandbox is an excellent pre-flight testing tool.

I run every new template or major content change through it first. The sandbox generates a detailed report: it gives me a SpamAssassin score and highlights exactly which spam-filter rules my email might be tripping; it checks that SPF, DKIM, and DMARC are all set up correctly and aligned; it validates my HTML/CSS to ensure there are no broken tags or code errors; and it checks all my links and images to flag any broken URLs or blacklisted domains.

I’ve also used GlockApps for inbox placement testing across multiple ISPs for example, testing the same campaign across Gmail, Outlook, and Yahoo to see whether it lands in the recipient’s inbox, Promotions, or spam, then comparing results before rollout (full comparison here).

SendForensics is another option for content quality scoring and spam filter predictions.

For list hygiene, I integrate verification services like ZeroBounce or Kickbox into my workflows to reduce bounce rates before they happen.

Ongoing deliverability monitoring

Once sending starts, I want real-time insight.

Mailtrap’s deliverability alerts run continuously in the background, alerting me instantly if bounce or complaint rates spike, or if delivery rates drop at a specific provider like Gmail or Yahoo. It also performs automated health checks and tracks long-term trends so I can see whether changes are improving or hurting performance. I have alerts integrated into Slack so my team can react within minutes, not days.

For enterprise-scale monitoring, platforms like Validity Everest or GlockApps Premium add seed list inbox placement reports, blocklist and spam trap monitoring, and deeper reputation analytics across dozens of providers. These tools can reveal subtle, provider-specific issues that don’t show up in aggregate metrics.

Finally, I maintain proactive blocklist monitoring through services like MXToolbox or HetrixTools, which scan multiple times daily for listings on Spamhaus, Barracuda, and other major lists. Early detection here can mean the difference between a quick fix and a weeks-long recovery.

To sum up

Ultimately, investing time and effort into these strategies and tools pays off the first time you avoid a major deliverability meltdown. By being proactive, detail-oriented, and quick to address issues, you can keep enjoying high deliverability instead of constantly fighting to get out of the spam folder.

For any email sender, the key is to stay vigilant and manage all these factors proactively. By following this comprehensive approach, you’ll maintain good email deliverability rate and keep your messages landing in subscribers’ inboxes where they belong.

Additionally, being a major part of the ROI equation, email deliverability revenue also impacts your final earnings.

So, I’ve decided to ask Mailtrap deliverability experts: 

• How deliverability affects revenue [click to jump ahead]
• What affects email deliverability [click to jump ahead]
• What some of the best deliverability practices are [click to jump ahead]

If you feel like freshening up or cementing your email deliverability knowledge, check out our dedicated article. ⬅️

Email deliverability revenue: a snapshot

Before we start, let me show you the results of the latest Validity report and how to calculate email deliverability ROI.

• Email deliverability benchmark

Hitting the primary inbox is a global challenge. As you can see from the table below, some countries, like South America and Brazil have an issue with emails going missing, while India has a problem with landing in spam. 

Only a handful of countries, such as Germany and France have over 90% deliverability rate with minimal spam and missing emails, which tells quite a story.

• Email deliverability ROI formula 

When it comes to calculating your email deliverability ROI, you need to know your total revenue from email and sending costs, which includes ESP fees, monitoring, staff, etc. the equation is as simple as it gets.

To calculate your email deliverability ROI, you need two numbers:

• Total revenue from email – All income generated by your email campaign(s).
• Total email costs – All expenses related to sending emails, such as ESP fees, monitoring tools, staff, etc.

The formula: ROI = (Total revenue from email – Total email costs) / Total email costs

For example, let’s say your total yearly revenue from email is $200,000 and your email costs are $25,000. Here’s how you would put the formula to work:

Step 1. Subtract your total yearly email costs from your total yearly revenue from email.

• $200,000 − $25,000 = $175,000 net profit from email.

Step 2. Divide the net profit from email by your total yearly email costs.

• $175,000 / $25,000 = $7

An ROI of 7 means that for every $1 you spend on email, you generate $7 in return.

How email deliverability affects revenue

Did you know that 2/3rds of businesses say deliverability is killing their revenue? Additionally, according to Validity’s research, deliverability costs the average email program over $15,000 per every million emails sent. 

To paint you a better picture instead of just handing out statistics, here’s a table that shows how deliverability affects revenue in a hypothetical scenario:

So, just a 10% increase in deliverability rate resulted in extra $4,350 in email deliverability revenue from one campaign. 

P.S. Interested in further exploring the impact of deliverability rate on the costs of your email marketing efforts? If yes, be sure to check out the awesome video our YouTube team has prepared on the topic!

What affects email deliverability

Typically, most major and common deliverability-related issues are related to:

• Email authentication
• Sender reputation
• Email list quality
• Email sending
• Email content 

Email authentication

Email authentication concerns security protocols such as SPF, DKIM, and DMARC, which essentially verify who you say you are when sending emails. They’re an industry-standard nowadays, and if you’re not authenticated, your emails won’t get accepted by the recipient’s email server.

How to improve: Set up SPF with your sending service, generate DKIM keys and enable signing, and publish DMARC policy starting with ‘none’ for monitoring. You can also use Mailtrap checkers for SPF, DKIM, and DMARC to ensure you’re properly authenticated.

Sender reputation

Sender reputation consists of:

• Email IP reputation, which is determined by the reliability of the sender’s IP address.
• Domain reputation, which is measured by ISPs based on the history of the sender’s address.

Getting marked as spam, hitting spam traps, people unsubscribing from your emails; these are only some of the things that impact your sender reputation.

If your sender reputation is not doing great, the chances are that ISPs will send your emails to spam, block them, or blacklist your IP or domain, directly influencing your deliverability rate. To check if you’ve been blacklisted, you can use Mailtrap’s free domain blacklist checker and IP checker.

How to improve: I recommend using Google Postmaster Tools or Microsoft SNDS, which allow you to observe the health of your IP and domain health. For instance, Mailtrap customers can share their Google Postmaster Tools with our deliverability experts so when we see something is off, we suggest the needed fixes and provide you with a peace of mind.

Email list quality

A quality email list makes a world of difference when it comes to deliverability. Creating one organically from scratch through double-opt in or permission-based forms will yield much better inboxing rates than one that’s been bought or scrapped. 

How to improve: Never buy email lists since it won’t only result in poor deliverability rates, but it might also cost you. Additionally, once you have a solid email list, make sure to keep it clean by implementing email validation logic, adding reCAPTCHA to your forms, and verifying emails.

Email sending

Taking care of your email sending configuration is half the battle won when it comes to deliverability. 

Take shared and dedicated IPs, for example. If you’re a high-volume sender and you’re using a shared IP, your deliverability will suffer since you’re using an address shared by multiple senders designed for low volume. However, with a dedicated IP, you’ll have more control used solely by you, giving you way better results.

Additionally, you need to warm up your IP and avoid sudden increases in volume since they’re a big red flag for ISPs. On top of that, if your recipients notice you’re sending more than usual, they’ll be more likely to mark you as spam or move you to the junk folder.

How to improve: If you want to work on your sending configuration or simply fine-tune it, I suggest hiring a deliverability consultant. On the other hand, if you’re on a budget or simply like doing things on your own, feel free to follow our in-depth guide on improving email deliverability. 👀

Email content

How many times have you opened your inbox, seen an email with a subject line that seems to be written by a five-year old (e.g., ACT FAST, LIMITED TIME OFFER or Re: your refund request) and reported it as spam? Starting from subject lines, how you write and design your emails plays a big role in whether your emails will go to junk.

This is especially true when it comes to HTML emails, which should perform well across different devices, have interactive features like forms and CTAs, include images, etc. A well-structured HTML email should engage your users, not improve your chances of getting marked as spam and negatively impact your deliverability. 

How to improve: Test your emails to make sure your HTML code is flawless and that your emails will pass spam filters. Additionally, I suggest using one of the many subject line testers out there to try out different subject lines and see what works best for each campaign. 

Email deliverability best practices

If you want to improve your email deliverability or keep it at a high rate, I recommend you to:

Perform regular audits

Email deliverability audit is the evaluation of the various factors that impact your deliverability. It measures whether your emails are reaching your recipients inboxes, where exactly they are landing, if they’re getting blocked, etc.

Typically, you should audit your email deliverability once a quarter or after each big campaign. Of course, this goes without saying, but you should also perform an audit whenever you notice a significant drop in metrics or change your infrastructure/ESP.

And here’s a summary of what you should audit:

Segment your email list

When you go to a supermarket, there are various isles that divide the market goods in categories like dairy products, water, meat, etc. The goods aren’t just stacked on top of each other, right?

What I’m getting to is that if you have an email list of, let’s say, 10,000 subscribers, you can’t just send the same email to them all. Not everyone on the list has the same needs or interests, is based in the same timezone, etc. Similarly to the supermarket goods, you need to segment your email list.

By grouping your contacts, you can target them more easily, which is going to improve not only your engagement, but your deliverability rates since you’ll be less likely to be flagged as spam.

Use an ESP with focus on email deliverability

Mailtrap is an Email Delivery Platform designed for product companies that plan to send a high volume of emails with high deliverability rates, in-depth analytics, and growth-focused features.

When it comes to email deliverability, Mailtrap can help you in the following ways:

• Deliverability features – Separate sending streams, dedicated IP addresses, email warm-up, throttling, and other advanced features for users to achieve high deliverability rates, regardless of the plan. 
• In-depth analytics – Helicopter view dashboards and drill-down reports for you to track opens, clicks, bounces, and more.

• Spam complaints – Our Deliverability Team systematically monitors the number of spam complaints and proactively assists customers with their issues to ensure compliance.
  • There’s also the free deliverability consultation with one of our experts. 
• Detailed Outlook stats – We provide you with performance breakdowns for each provider, including Outlook. These are open rates, spam rates, bounces, etc.

• Email authentication – We require each sender to have proper authentication (SPF, DKIM, DMARC) before they start to send so each domain is properly checked and prepared.
• Dedicated Bulk Stream – Our Bulk Email Service is designed for high-volume senders and can handle large amounts of emails without a stutter, all the while keeping your deliverability high.
  • To each email you send through the Bulk stream, we automatically add a one-click unsubscribe button.

Comply with email marketing laws

Email marketing laws are designed to protect user privacy and data, prevent spam, but also that businesses send their emails to people who have consented to them. 

Complying with these laws not only ensures you don’t get penalized by ESPs and ISPs, it will also ensure you don’t need to pay any fines. For example, if you don’t comply with the CAN-SPAM Act, you’ll have to pay a fine of up to $44,000.

Here’s a quick summary of all the relevant email marketing laws (click on the link for more details): 

Meet the inbox provider requirements

Besides the email marketing laws, there are also requirements and regulations set by inbox providers like Gmail, Microsoft, Yahoo, and Apple Mail.

Although these might not seem important on paper, the fact is that in 2024, inbox placement rates for Gmail averaged 89.8%, whereas they declined to 84.2% later during the year after Google implemented requirements. The story is similar for other inbox providers, too.

For your convenience, I’ve summed them up in a table, but nonetheless, make sure to go through the official documentation if you plan to comply:

Monitor your metrics

The most important email marketing KPIs related to email deliverability are performance metrics, which tell you how your campaigns are performing. Following them closely, you can see fluctuations (if any), implement the necessary changes, and improve your deliverability.

Here’s what Mailtrap deliverability experts recommend:

Use email deliverability tools

With the vast abundance of email deliverability tools out there nowadays, there really isn’t a reason not to use them to make sure your emails land in recipients’ inboxes.

For instance, you can use the free MxToolbox to assess your DNS records or analyze headers. Or, you can use full-fledged deliverability platforms like Everest by Validity or GlockApps to optimize your infrastructure. 

For a comprehensive list of 15 deliverability we tested and used over the years, check out our dedicated guide. ⬅️ 

Conclusion

With that, we’ve reached the end of our email deliverability revenue guide! 

To recap: if you don’t want your ROI to take because your deliverability rate drops, authenticate your emails, make sure your sender reputation is spotless, grow your lists organically, configure your sending configuration, and test your emails. 

Most importantly, partner with an ESP that will help you reach high deliverability rates, instead of holding you back. And yes, I’m hinting at Mailtrap. 🙂

Happy sending! 

Further reading:

• Email Deliverability Comparison Results [2025]
• Performing an Email Sending Reputation Audit
• Using Email IP Pools for Higher Email Deliverability 

If not…

1. Your marketing campaigns go unseen. 
2. Your transactional emails fail to reach their destination. 
3. Your efforts translate into lost revenue and damaged sender reputation.

At Mailtrap, we help you improve deliverability with your organically built audience, whether it’s for marketing campaigns or critical transactional communications. 

This comprehensive guide walks you through the essential strategies and best practices that high-volume senders use to achieve optimal inbox placement and maximize their email ROI. 

If you’re a business grappling with these challenges, consider a deeper dive with our experts. ⬇️

How to improve email deliverability: a snapshot

Achieving high email deliverability is an ongoing process that requires a strategic approach across technical setup, sender reputation, list management, and content optimization. 

Here’s a quick overview of the quick wins we’ll explore in detail:

Email deliverability improvement strategies

Achieving consistent inbox placement for your high-volume sends demands a multi-faceted approach. 

• Email infrastructure setup
• Sender reputation
• email list quality
• email sending 
• email content quality
• email user engagement

I will break down each aspect into an actionable how-to. Let’s start with the technical improvements.

Improve email infrastructure

To improve email infrastructure, you need to focus on email authentication, domain configuration, and email security.

It will show Internet Service Providers (ISPs) and mailbox providers that your emails are legitimate and secure. And actually, all major ISPs require authentication protocols if you’re to be considered a legitimate sender ➡️(Gmail, Outlook, Yahoo, and Apple Mail). 

I’ll explain what you should check in your current setup, why this matters, and what steps you need to take to improve your inboxing rates.

Email authentication protocols

Double-check the protocols’ setup and fix the following if you identify any issues. 

• SPF (Sender Policy Framework): Check your SPF record with Mailtrap’s Free SPF Record Checker. If an email originates from a server not listed in your SPF record, it’s likely to be flagged as suspicious or spam.
• DKIM (DomainKeys Identified Mail): Utilize Mailtrap’s Free DKIM Record Checker to validate your setup.
• DMARC (Domain-based Message Authentication, Reporting & Conformance) builds on SPF and DKIM. For large senders, it helps gain visibility into spoofing attempts. Use our Free DMARC Record Checker to ensure that DMARC is correctly configured.
• BIMI (Brand Indicators for Message Identification): Display your brand’s logo next to your authenticated emails in the recipient’s inbox. While not directly a deliverability protocol, BIMI enhances brand recognition and user trust, indirectly boosting engagement. 

For a deeper dive into authentication, refer to our guide on Email Authentication Explained: SPF, DKIM, DMARC, BIMI.

DNS records for email sending

Proper DNS configuration ensures your email servers are correctly identified and email can be routed effectively. So, here’s your homework 😀

• rDNS (Reverse DNS or PTR records): Maps an IP address back to a domain name, acting as a “reverse lookup.” ISPs often check PTR records to ensure the sending IP is legitimate and not a generic or dynamic address, which helps prevent spam.
• MX records (Mail Exchange records): Specify the email servers responsible for accepting email messages on behalf of your domain. Okay, these are primarily for inbound email, but correctly configured MX records indicate a professionally managed domain, lending credibility to your outbound emails.

Custom domain configurations

Use custom configurations instead of the generic ones provided by your Email Service Provider. Here are the customizations to make. 

• Custom return path (MAIL FROM): Use a custom subdomain (e.g., bounces.yourdomain.com) for your return path to ensure that bounce handling doesn’t negatively impact your main sending domain’s reputation and allows for easier tracking.
• Custom tracking URLs: If your ESP uses tracking links (for opens, clicks), ensure these are branded with your domain (e.g., clicks.yourdomain.com). This avoids sharing reputation with your ESP’s generic tracking domain and instills greater trust in recipients and filters.

Email transmission security standards

Secure emails in transition to protect sensitive data and signal trustworthiness to mailbox providers. This is what to do 🔽

• TLS (Transport Layer Security) / STARTTLS: Most ISPs require and prefer TLS connections. You should always enforce STARTTLS where possible.
• MTA-STS (Mail Transfer Agent Strict Transport Security): A security standard that forces email servers to use TLS when sending email. It helps prevent downgrade attacks where an attacker might force a connection to use unencrypted channels. Mailtrap’s blog has an in-depth guide on the Mail Transfer Agent (MTA) Explained.
• TLS-RPT (TLS Reporting): Companion to MTA-STS, TLS-RPT allows you to receive reports on TLS connection issues, providing visibility into potential security problems that could affect deliverability.

Further reading: STARTTLS vs SSL vs TLS Explained

Mailbox provider Feedback Loop (FBL)

Subscribe to FBLs (e.g., through Google Postmaster Tools or Microsoft SNDS) to quickly identify and remove complainers from your list. Of course, this prevents further complaints that damage your reputation. 

For more details on the feedback loop, check: What Is Email Feedback Loop and Why Is It Important?

Email Headers

Properly configured email headers provide necessary information for email servers and can influence how your emails are processed and delivered.

• Message ID: Most times, it’s automatically generated. However, ensure it’s correctly formatted and present to help with email tracking and debugging.
• Date header: Accuracy here is important for chronological sorting and filter evaluation. So, check these headers particularly if you operate in different time zones. 
• List-unsubscribe header: Make sure this header provides a one-click unsubscribe option directly within the email client interface. New sender requirements mandate it, and it genuinely helps with spam complaints. Learn more about its importance: List Unsubscribe Header: Why and How to Use.
• Precedence header: Used to indicate the nature of an email (e.g., precedence: bulk or precedence: junk) to inform receiving servers that it’s a bulk email and should not generate auto-replies. While less common now, it can still have an impact.

Use a reliable email service provider

If you handle transactional and marketing campaigns at a volume, a reliable Email Service Provider (ESP) is essential. Check whether the ESP provides the necessary technical infrastructure to ensure your emails consistently reach recipients’ inboxes.

For instance, Mailtrap Email API/SMTP offers a robust infrastructure designed for high-volume senders. We focus on maximum throughput and optimal inbox placement by leveraging the following:

• Automatic email authentication: Mailtrap configures and manages essential authentication protocols (SPF, DKIM, DMARC). This process verifies your emails as legitimate, significantly reducing the likelihood of them being flagged as spam or rejected by receiving servers.

• Dedicated sending streams: Mailtrap provides separate, isolated sending streams for different email types (e.g., transactional vs. marketing). This prevents potential deliverability issues from spilling from one email type to another (marketing to transactional and vice versa).

• Robust security and compliance: We are compliant with regulations such as ISO 27001 and GDPR, ensuring your data and your recipients’ privacy are protected.

All in all, we aim to take the headache out of email deliverability. Let Mailtrap simplify your email infrastructure so the emails land where they belong 🔽

Improve sender reputation

Your sender reputation encompasses your IP reputation and domain reputation. It’s a critical factor ISPs use to determine whether your emails reach the inbox or are sent to the spam folder. Check the key aspects you need to consider. 

IP reputation management

The reputation of the email-sending IP address (or addresses) directly impacts your deliverability. Here’s what to keep in mind. 

• Shared vs. dedicated IP:
  • Shared IP address: When choosing an ESP, make sure they adhere to the security protocols and have internal mechanisms to weed out spammers. Ideally, like Mailtrap, the provider should offer separate sending streams for different types of messages.
  • Dedicated IP address: If you send more than 100K emails a month, I’d encourage you to choose a dedicated IP address. It gives you complete control over the IP reputation and allows for more precise IP warming. You can check more on the topic: Shared vs Dedicated IP in Email Sending.
• IP warming & re-warming: When you get a new dedicated IP or significantly change your sending practices (like introducing a new domain, subdomain, or a third-party service for cold emails), you must gradually increase your sending volume. This is the IP warm-up, building trust with ISPs over time. Re-warming is necessary if you have periods of inactivity or significant changes in volume. 

• IP pooling strategies: If you send at high volumes (e.g., 1M+ emails a month) or have diverse email streams, use multiple dedicated IPs grouped into “IP pools.” This strategy allows you to distribute the sending load and isolate different types of email (e.g., transactional vs. marketing) to separate IPs, protecting the reputation of critical streams.
• IP segmentation by email stream (Reminder): Send different types of emails (e.g., transactional, marketing, notifications) from separate dedicated IPs or subdomains to isolate their reputations. If your marketing emails encounter issues, your critical transactional emails remain unaffected. 
• IP blocklist monitoring: Regularly check if your sending IPs have been listed on any public or private blocklists. ISPs use these lists to identify and block email from suspicious sources. You can use Mailtrap’s Free IP Blacklist Checker to monitor your IP status.
• IP delisting process: If your IP gets blocklisted, promptly follow the delisting procedures of the specific blocklist provider. This typically involves identifying and rectifying the root cause of the listing (e.g., spam complaints, spam traps) and then requesting removal.

Email domain reputation management

Similar to your IP, the reputation of your sending domain is crucial because it represents your brand’s trustworthiness, which is often expressed through a sender score.

• Domain warming techniques: As a reminder, new sending domains or subdomains benefit from a gradual increase in sending volume, especially to highly engaged recipients.
• Subdomain strategy for isolation: Using distinct subdomains for different email streams (e.g., marketing.yourdomain.com, transactional.yourdomain.com, newsletter.yourdomain.com) allows you to compartmentalize reputation. If marketing.yourdomain.com faces email performance issues, transactional.yourdomain.com remains unaffected.
• Google Postmaster Tools insights: This free tool from Google provides valuable data on:
  • Your sending domain’s reputation 
  • IP reputation 
  • Spam rate 
  • Authentication and delivery errors for Gmail recipients. 

Regularly monitoring these insights is critical for proactive reputation management. 

• Microsoft SNDS data usage: Microsoft’s Smart Network Data Services (SNDS) provides similar insights for Outlook.com and other Microsoft properties. It offers data on spam complaints, filtered emails, and overall reputation, helping you troubleshoot deliverability issues specific to Microsoft inboxes.
• Consistent domain branding: Ensure your “From” address, custom tracking domains, and custom return-path domains all consistently use your primary sending domain or closely related subdomains. This consistency builds brand recognition and trust. You can also use Mailtrap’s Free Domain Blacklist Checker to monitor your domain’s status.

Recipient engagement impact on reputation

Recipient engagement is a powerful signal to ISPs about the quality and relevance of your emails. High positive engagement boosts your reputation, while negative email engagement can quickly degrade it.

• Positive engagement signals: Keep an eye on opens, clicks on links within the email, replies, marking an email as “not spam,” and adding your “From” address to their address book. ISPs interpret these actions as signs that recipients value your emails.
• Negative engagement signals: The most damaging are spam complaints. Other negative signals include deleting emails without opening them, unsubscribing, and emails bouncing back as undeliverable.
• Engagement-based segmentation: Segment your email list based on engagement levels (e.g., highly engaged, moderately engaged, inactive). Send your most valuable content to your most engaged segments to reinforce positive reputation signals. Also, create reengagement campaigns to motivate other, less-engaged segments. 
• Effective sunset policies: Implement policies to gradually reduce or stop sending to consistently unengaged subscribers. Sending to inactive users generates low engagement and can accumulate negative signals over time, harming your overall deliverability, particularly if you send a large volume of emails.

Reputation recovery strategies

If your sender reputation takes a hit, a systematic approach is needed for recovery. So, don’t panic, but do the following.

• Diagnose root cause of damage: Identify why your reputation suffered. Was it a sudden spike in spam complaints, high bounce rates, or a blocklisting? Utilize tools like Google Postmaster Tools, SNDS, and DMARC reports to pinpoint the issue.
• Create a step-by-step recovery plan: This might involve pausing sends, removing problematic subscribers, re-engaging cautiously, or appealing blocklist entries.
• Communication with ISPs/blocklist owners: In some cases, direct communication with the relevant ISP postmaster teams or blocklist operators may be necessary after you’ve addressed the underlying issues. Be prepared to explain the steps you’ve taken to resolve the problem.
• Gradual re-warm and ramp up the volume: Reestablish your sending reputation slowly after addressing the root cause. Begin with highly engaged segments and gradually increase volume, monitoring email deliverability rate closely. This is similar to the initial IP warming process, but with an added focus on demonstrating sustained good behavior. 

Improve email list management

Your email list is your most valuable asset in email marketing. Maintaining its quality and relevance is essential for consistently good email deliverability. Here, I will explain what you should do to improve the quality of your email list and why you should do it. 

Optimize list acquisition methods

The journey to high deliverability begins the moment you acquire a subscriber, where quality over quantity is the golden rule. So, when a new subscriber comes knocking on your door, focus on the following.

• Permission-based opt-ins: Always ensure you have explicit permission from every subscriber. This means they’ve actively agreed to receive emails from you. Avoid any pre-checked boxes.
• Clear consent mechanisms (GDPR focus): The opt-in forms must clearly state what the subscriber is signing up for, how often they’ll hear from you (e.i, the number of emails per week/month), and what kind of content to expect. For users in regions with strict data protection laws like GDPR, ensure consent is freely given, specific, informed, and unambiguous. (To stress, it’s a legal requirement, not a nice-have 😀)
• Transparent data usage statements: Clearly communicate your privacy policy and how subscriber data will be used (data security at rest and in transit). This builds trust and sets expectations, reducing the likelihood of spam complaints later.
• Source quality validation: Implement processes to monitor and validate the source of your new subscribers. This helps identify and eliminate any channels that might inadvertently bring in low-quality or non-consenting leads.
• Avoiding purchased or rented lists: Never! Lemme say that again, NEVER 😀, under any circumstances, purchase or rent email lists. These lists are notorious for containing spam traps, inactive addresses, and non-consenting users, leading to immediate and severe damage to your sender reputation and deliverability.

Implement effective opt-in processes

The method you use to onboard new subscribers directly affects the quality and engagement of your list. Therefore, I’d like to dissect opt-ins further to give you an actionable framework you can apply right away.

• Single opt-in (SOI) vs. double opt-in (DOI) strategies:
  • Single opt-in (SOI): Subscribers are added to your list immediately after filling out a form. While quicker for the user, it carries a higher risk of invalid addresses or accidental sign-ups.
  • Double opt-in (DOI): Subscribers receive a confirmation email that they must click to verify their subscription. This is the gold standard for high-volume senders, as it guarantees consent, confirms email validity, and leads to significantly higher engagement and deliverability rates.

• DOI confirmation email design and timing: Your DOI email should be clear, concise, and sent immediately after sign-up. Its design should be simple, with a prominent call-to-action to confirm the subscription. It’s a transactional email, actually. 
• Managing and storing consent records: Maintain auditable records of when and how each subscriber provided consent. This is crucial for compliance with data protection regulations and for demonstrating legitimacy to ISPs if questioned.
• Welcome email for new subscribers: Send a timely welcome email to new subscribers. This reinforces their decision, sets expectations, and provides initial value, kickstarting positive engagement.

Advanced list hygiene techniques

Proactive list cleaning is vital to prevent bounces, reduce spam complaints, and protect your sender reputation from degradation.

So, buckle up and employ the following email deliverability best practices:

• Automate hard bounce removal rules: Implement automated systems to remove hard-bounced email addresses from your list immediately. Hard bounces indicate permanent delivery failures and negatively impact your reputation. For more on this, see Email Bounce Explained: Definition, Reasons, Best Practices
• Monitor soft bounces and establish retry logic: Monitor soft bounces (temporary delivery issues) and implement a retry strategy (e.g., a couple of retries in an hour or two after the initial bounce). If an address soft bounces repeatedly, consider temporarily suppressing or removing it after a defined number of failures. Check out our blog post to learn more about the Difference Between Hard and Soft Bounce.
• Detect and mitigate spam traps proactively: Spam traps are invalid email addresses used by ISPs to identify spammers. Hitting them severely damages your reputation. Regularly clean your list and scrutinize acquisition sources to avoid them. For more details, read ➡️ What is a Spam Trap: Guide for Email Marketers and Software Developers.
• Using list validation and cleaning services: Consider using third-party email list validation and cleaning services for large lists. Better yet, if you got programming skills or have a dev team to back you, consider baking an API validation and sanitization into your lead-capture backend. Whichever way, these tools can identify invalid, risky, or low-quality email addresses before you send to them. Read our expert tips on Email List Cleaning: Best Practices from an Expert.

Strategic list segmentation for relevance

Segmentation improves deliverability by ensuring your emails are relevant to your audience, leading to higher engagement.

• Segmentation by engagement levels: Yeah, I know, I begin sounding like a broken record. But anyway, group subscribers based on their interaction with your emails (e.g., highly engaged, moderately engaged, unengaged). This allows you to tailor content and sending frequency.
• Demographic and psychographic segmentation: Segment based on subscriber demographics (age, location) or psychographics (interests, values) to deliver more targeted content.
• Behavioral segmentation (website activity, purchase history): Create segments based on user behavior on your website, purchase history, or in-app actions. This enables highly relevant, triggered, or personalized communications.
• Dynamic list segmentation techniques: Implement systems that automatically update segments based on real-time user behavior, ensuring your lists are always current.
• Personalization based on segments: Leverage your segmentation data to personalize email templates, content, subject lines, and offers, making each email feel more tailored to the individual. For a full tutorial, check ➡️Email List Segmentation Explained: Tutorial with Examples.

Enhance subscriber preference and unsubscribe handling

Providing clear, easy-to-use options for managing preferences and unsubscribing is crucial for maintaining a healthy list and avoiding spam complaints.

• Implementing user preference centers: Allow subscribers to choose the types of content they receive and the frequency. This empowers them and reduces the likelihood of unsubscribes due to irrelevant content or excessive frequency.

• Prompt and compliant opt-out processing: Process unsubscribe requests immediately without requiring additional steps (like logging in). Failure to do so can lead to spam complaints and legal non-compliance (e.g., CAN-SPAM, GDPR).
• Manage global suppression lists: Maintain a comprehensive global suppression list of all unsubscribed or bounced addresses (ideally, one correctly parsed list across all domains and subdomains you use). This ensures you never accidentally re-add or send to contacts who have opted out or are undeliverable. Here’s a comprehensive guide on How to Manage Your Email Suppression List effectively.

Maintain ongoing data quality and compliance

List management isn’t a one-time task; it’s a continuous commitment to data quality and legal compliance. 

• Periodic data accuracy audits and updates: Regularly audit your list for outdated information and implement processes for subscribers to update their own details.
• Processes for data subject rights (Access, Rectification, Erasure under GDPR): For global senders, establish clear procedures for handling data subject requests as per regulations like GDPR, including access to their data, rectification of inaccuracies, and the right to be forgotten.
• Staying updated on email marketing regulations: Email regulations (like CAN-SPAM, GDPR, CCPA, and new ISP requirements from Google and Yahoo) are constantly evolving. Stay informed to ensure your practices remain compliant and legal infringements don’t negatively impact your deliverability.

For more guidelines on legal conundrums, go to: Legal Aspects of Email Marketing: Laws, Compliance, and Penalties 

Improve email sending practices

Beyond technical setup and list hygiene, how you send your emails—your volume, frequency, and timing—plays a significant role in your deliverability and reputation with ISPs. 

Let’s take a look at what you can adjust to achieve a higher inbox placement rate.

Manage sending volume and consistency

ISPs favor senders with predictable and consistent sending patterns. Sudden, unexplained spikes in volume can trigger spam filters.

• Establish consistent, predictable sending patterns: Aim for regular sending schedules. If you typically send weekly newsletters, try to stick to that pattern. Consistent volume helps ISPs learn and trust your sending behavior.
• Avoiding sudden large volume spikes: Unexpected increases in email volume can look suspicious to ISPs, even for established senders. If you anticipate a major campaign, prepare by gradually increasing your volume beforehand, similar to IP warming. Monitor your deliverability metrics closely during ramp-up phases to catch any issues early.

Optimize sending frequency and cadence

Finding the “just right” frequency keeps your audience engaged without leading to list fatigue or spam complaints. How to do it? My best tip is to experiment to determine… 

• Optimal email frequency per list segment: It’s not uncommon for different segments of the audience to tolerate different sending frequencies. Analyze engagement data for each segment to fine-tune how often you send to them.
• Tactics to avoid list fatigue: The way to do it is just don’t email unsegmented recipients often. To that, you need to hawk over open rates and unsubscribe rates – a drop often signals fatigue. The same goes for a sudden increase in inactive subscribers. 
• The impact of sending cadence on engagement and deliverability: Continuously test and analyze how changes in your sending cadence affect key metrics like open rates, click-through rates, and, crucially, spam complaint rates and deliverability. If you see spikes in negative engagement, your recipients may prefer a slower tempo.

Utilize email throttling and rate limiting effectively

Throttling and rate limiting prevent you from overwhelming an ISP’s receiving servers, which can lead to deferrals or blocks. Anyway, you need to do some homework and some tweaking to get it right. Here’s a set of bullets to get you going.

• Understand ISP receiving limits and feedback: Typically, the receiving limit is around 3,600 emails per hour. Exceeding these limits often results in temporary rejections (soft bounces) or, worse, hard blocks.
• Configure send speed (throttling) in ESP/MTA: Your Email Service Provider (ESP) or Mail Transfer Agent (MTA) should allow you to configure sending rates. Properly setting these limits helps you stay within ISP boundaries. 
• Benefits of throttling for high-volume sends: Throttling is a technical practice that controls the rate at which emails are sent over a given period rather than sending a large volume all at once. It ensures your emails are accepted gracefully by ISPs, preventing backlogs and delivery errors, leading to smoother, more consistent deliverability.

Strategic email stream separation

Separating different types of email traffic is a cornerstone for maintaining a good reputation for high-volume senders. But how you separate it depends on your ESP and the email volume. Not all providers offer separate streams. And sometimes, it makes more sense to use a separate dedicated IP on top of separate streams, particularly if you do outreach. 

So, check the method to this streaming madness 😀

• Rationale for separating transactional vs. marketing email streams: Transactional emails (e.g., password resets, order confirmations) are expected and critical, while marketing emails are often seen as less urgent. Mixing these can put your critical transactional deliverability at risk if marketing sends face issues.
• Using dedicated IPs/subdomains for different email types: As mentioned in IP and domain reputation, assigning separate dedicated IPs or subdomains for transactional, marketing, and notification emails allows each stream to build and maintain its own reputation independently.

Leverage Send Time Optimization (STO)

Sending emails when your audience is most likely to engage can significantly boost open and click rates, positively impacting deliverability.

• A/B testing send times for different audience segments: Experiment with various send times and days of the week to pinpoint what works best for specific segments.
• Utilizing ESP built-in STO features vs. manual analysis: Many ESPs offer built-in STO features that automatically deliver emails at the optimal time for each recipient. For custom setups, detailed analysis of your own metrics is key.
• Considering time zones for global audiences: If you have a global audience, ensure your send times are optimized for their respective time zones to maximize engagement.

Best practices for email batching and campaign scheduling

You need to properly break down (segment) and schedule large email campaigns. And large, in our experience, typically translates to 10K or more emails a week. 

Otherwise, the almost willy-nilly approach can influence how ISPs perceive you as a sender. More importantly, it limits your ability to monitor performance across different funnel stages. 

So, here’s what to do. 

• Break down large campaigns into smaller batches: Instead of sending a million emails all at once, divide the campaign into smaller, manageable batches. This allows for smoother delivery and easier identification of issues if they arise.
• Intelligent scheduling strategies across peak/off-peak hours: Schedule non-critical bulk sends during off-peak hours for ISPs when their servers might be less congested. Prioritize critical transactional sends during peak times if deliverability is paramount.
• Prioritize critical transactional emails over bulk sends: Ensure your MTA or ESP prioritizes transactional emails in its queue. These are often time-sensitive and have the highest deliverability requirement.
• Monitoring send progress and server responses during large sends: Actively monitor your sending progress and any error responses from receiving servers during large campaigns. This proactive approach allows you to identify and react to potential issues (like throttling or deferrals) in real-time.

Improve email content

Poor content can land your emails in the spam folder, even with the perfect technical setup and a pristine list. So, focus on building trust with the content and avoid triggering spam filters.

Check the hands-on tips and tricks below. 

Optimize subject lines and preheaders for engagement and filters

Your subject line and preheader are the gatekeepers to your email’s content. In a lot of cases, they determine if your email is opened or ignored (or worse, marked as spam).

• Avoid common spam trigger words and ALL CAPS: Steer clear of words and phrases commonly associated with spam (e.g., “free money,” “guarantee,” excessive exclamation marks) and avoid using all capital letters, which can appear aggressive and spammy. 

To be perfectly honest, Yaroslav, our in-house deliverability expert, identified less of an impact of “spammy” words on campaign performance. However, this finding shouldn’t motivate you to create emails like you’re selling snake oil. 

If you need more details and examples of best practices, our guide on 240 Email Spam Words To Avoid When Sending Emails can provide a helpful reference.

Or maybe you want to ⬇️📲…

• Craft clear, concise, and relevant subject lines: Your subject lines should accurately reflect the email’s content, be brief, and clearly communicate value to the recipient.
• Use personalization effectively (names, interests, etc.): If possible, incorporate a recipient’s name or interests into the subject line. This can significantly boost open rates, as it makes the email feel more relevant.
• Maximize preheader text for additional context and intrigue: The preheader text (the snippet of text visible after the subject line in the inbox) should complement your subject line, providing more context or a compelling reason to open.
• A/B test subject lines and preheaders for open rates: Continuously test different subject line and preheader combinations to identify what resonates best with your audience and drives higher open rates. 

Write email body copy that builds trust and avoids filters

The body of your email must deliver on the promise of your subject line and maintain recipient trust.

• Balance promotional content with informational/value-driven text: For marketing emails, balance promotional messages with genuinely helpful, informative, or entertaining content. This builds long-term engagement and trust.
• Implement advanced personalization within the body: Go beyond just a name. Use behavioral data, purchase history, or other subscriber attributes to dynamically populate content within the email body, making it highly relevant.
• Ensure proper grammar, spelling, and professional tone: Typos, grammatical errors, and an unprofessional tone can undermine your credibility with recipients and spam filters. Always proofread diligently.

Design HTML emails for optimal deliverability and user experience

A well-coded, responsive HTML email formatting is crucial for a positive user experience, and it helps bypass spam filters.

• Use clean, lightweight HTML code: Complex or broken HTML can trigger spam filters or render poorly. Use clean, minimalist, and standards-compliant code. Avoid excessive inline styling or large amounts of hidden text. Our Free HTML & CSS Email Checker by Mailtrap can help you validate your code.
• Ensure fully mobile-responsive email design: A significant portion of emails are opened on mobile devices. Your emails must render perfectly on all screen sizes to ensure readability and engagement.
• Maintain a healthy text-to-image ratio (avoiding image-only emails): Emails that are primarily images with little text are often flagged by spam filters as they can be used to hide malicious content. Aim for a balanced ratio, with sufficient text. For instance, about 80-20% split in favor of the text. 
• Implement ALT text for all images (accessibility and deliverability): Always include descriptive ALT text for your images. This improves accessibility for visually impaired users and provides context if images fail to load.
• Basic email accessibility considerations (WCAG): Beyond ALT text, consider other accessibility best practices (e.g., sufficient color contrast, logical reading order) to ensure your emails are usable by everyone.

Manage links and attachments responsibly

How you handle links and attachments can significantly influence how spam filters perceive your email.

• Link exclusively to reputable and secure (HTTPS) domains: Ensure all links in your email point to legitimate, trustworthy websites secured with HTTPS. Linking to suspicious or unencrypted domains is a major red flag.
• Avoid an excessive number of links or link shorteners known for abuse: Too many links can appear spammy. Also, be wary of generic link shorteners often abused by spammers; branded shorteners are safer. But generally, I’d say avoid shorteners unless absolutely necessary. 
• Minimize or avoid attachments in marketing/bulk emails: Attachments are a common vector for malware and are almost always flagged in bulk emails. Avoid them in marketing campaigns entirely. For transactional emails that require attachments, ensure they are absolutely necessary and secure, something like invoices, bills, shipping documents, etc.
• Use clear, descriptive anchor text for hyperlinks: Use descriptive anchor text for your links rather than generic phrases like “click here.” This improves user experience and signals legitimacy.

Set clear Calls-to-Action (CTAs) and compliant unsubscribe options

Your CTAs should be unmistakable, and your unsubscribe options even more so.

• Design clear, prominent, and compelling CTAs: Make it easy for recipients to understand what action you want them to take and where to click. Use compelling language and visually distinct buttons. 
• Make the unsubscribe link easy to find, understand, and use (one-click): This cannot be stressed enough. A clear, easily accessible unsubscribe link (usually in the footer) is crucial for avoiding spam complaints.
• Technical implementation of list-unsubscribe header: As previously discussed, implementing the List-Unsubscribe header allows users to unsubscribe with a single click directly from their email client, dramatically reducing complaint rates. For detailed steps on how to avoid emails going to spam, check out our tutorial: How to Avoid Emails Going to Spam: Tutorial.
• Honoring unsubscribe requests as per regulations (GDPR, CAN-SPAM): Immediately process all unsubscribe requests. Delaying this or making it difficult is a clear violation of email marketing laws and will severely damage your sender reputation.

Pro Tip: According to the regulations mentioned above (GDPR, CAN-SPAM), you have up to 10 days to honor the requests. However, users expect it to be immediate, or at least, effective in 24-48 hours. Given the automatic nature of most contemporary email platforms, my suggestion is to delist a recipient as soon as they opt out with a basic trigger-action automation. 

Improve email user engagement

Ultimately, deliverability is about consistently landing in the inbox because recipients want your emails. Here’s how to softly nudge users towards engagement. 

Maximize positive engagement signals

As mentioned a few times, positive interactions with your emails are highly valued by ISPs. Encouraging these helps build a robust sender reputation. So, consider employing the following. 

• Encourage replies and forwards: Emails that generate replies or are forwarded indicate high value. Craft content that sparks conversation or is highly shareable.
• Get emails marked “Important” or moved to the primary inbox: Encourage recipients to manually mark your emails as important or move them from promotions/spam folders to their primary inbox. This is a very strong positive signal to mailbox providers. However, make sure to do it sensibly – for instance, only when a recipient reports your newsletter is getting into the Promotions tab, or elsewhere. 
• Promote “Add to Contacts” / whitelisting: Encourage subscribers to add your “From” email address to their address book or whitelist. This virtually guarantees future deliverability. Again, this is something you need to do tactfully, not like a full-on campaign focused on “Add to Contacts.” 

Minimize negative engagement signals

Negative interactions can quickly degrade your sender reputation, making it harder to reach the inbox.

• Tactics to reduce spam complaints: The most critical tactic is ensuring clear, informed consent during list acquisition. Beyond that, consistently providing valuable, relevant content and offering an easy, one-click unsubscribe option are paramount. 
• Avoiding “delete before reading”: When recipients consistently delete your emails without opening, it signals disinterest to ISPs. Strong sender recognition and consistently valuable, intriguing subject lines are crucial to avoid this.

Drive engagement with advanced personalization and segmentation

Tailor your communication to make emails more relevant, leading to higher engagement and better deliverability. Here are the pointers. 

• Use behavioral triggers for highly relevant, timely emails: Implement email automation based on user actions (e.g., abandoned cart reminders, post-purchase follow-ups). These triggered emails are highly relevant and often have exceptional engagement rates.
• Implement dynamic content based on user data and preferences: If possible, leverage your ESP’s capabilities to insert dynamic blocks of content into emails based on individual subscriber data, preferences, or behavior.
• Personalization techniques beyond basic merge tags: Go beyond just using a recipient’s first name. Incorporate purchase history, browsing behavior, lifecycle stage, or product recommendations for deeper personalization. 

Enhance content value and relevance to boost interaction

The intrinsic value of your email content is the ultimate driver of engagement.

• Provide exclusive content or early access: Offer your email subscribers unique benefits or information unavailable elsewhere. This incentivizes opens and clicks.
• Use storytelling and creating emotional connections: Engaging narratives and content that resonates emotionally can significantly increase the reading time and the likelihood of interaction.
• Ensure a clear value proposition in every email: Before sending, ask yourself: “What value does this email provide to the recipient?” Make that value proposition clear and compelling.
• Align email content with the subscriber’s journey stage: Ensure the content matches where the subscriber is in their customer journey (e.g., onboarding, consideration, loyalty).

Optimize send timing and frequency for peak engagement

Even the most perfect email can be missed if sent at the wrong time.

• A/B test different send times and days of the week: Continuously experiment with various send times and days to identify when your audience segments are most active and receptive.
• Utilize Send Time Optimization (STO) tools or features: Many ESPs offer STO capabilities that use algorithms to predict the best send time for each individual recipient based on their past engagement patterns.
• Respect user-stated frequency preferences (via a preference center): If you offer a preference center (as discussed in Enhancing subscriber preference and unsubscribe handling), rigorously adhere to the frequency choices made by your subscribers.
• Adjust sending cadence based on individual engagement levels: For unengaged segments, reduce sending frequency or pause sends altogether to avoid negative signals and potential spam complaints.

Incorporat interactive elements and direct feedback (Advanced tactic)

For tech-savvy senders, interactive elements can supercharge engagement. Mind you that some of these actions may require you to have decent programming skills. Or simply, you can ask a developer for help. 

• Explore AMP for email for in-mail actions (polls, forms): AMP (Accelerated Mobile Pages) for email allows recipients to complete actions like filling out forms, answering polls, or browse products directly within the email client, without leaving their inbox.
• Embed simple surveys or polls for feedback: Directly ask for feedback within the email to gauge satisfaction or gather insights(e.i. You could use open-ended questions with a small incentive for the participants). This demonstrates you value their opinion and encourages interaction.

Email deliverability monitoring: your continuous feedback loop

Without consistent tracking of key metrics, you’re sending emails into a void, unaware of how they’re truly performing. For high-volume senders, this means having robust systems in place to provide real-time insights and diagnostics.

Key deliverability metrics to track

To maintain a healthy email program and ensure your emails reach the inbox, focus on these critical metrics:

• Inbox placement rate: This is the ultimate metric. It tells you the percentage of your emails that successfully land in the primary inbox, as opposed to the spam folder, promotions tab, or being rejected entirely.
• Open rate: While not a direct deliverability metric, a consistently low open rate can signal engagement issues that may eventually affect your sender reputation. It indicates whether your subject lines and sender name are resonating.
• Click-Through Rate (CTR): Similar to open rates, a healthy CTR indicates that your content is relevant and valuable, which positively influences engagement signals.
• Bounce rate: Track hard bounces (permanent delivery failures) and soft bounces (temporary issues). High bounce rates, especially hard bounces, severely damage your sender reputation. Automated removal of hard bounces is non-negotiable.
• Spam complaint rate: This is one of the most damaging metrics. A high rate indicates that recipients are actively marking your emails as spam, which significantly degrades your sender reputation with ISPs. Aim for rates well below 0.1%.
• Unsubscribe rate: While not as damaging as spam complaints, high unsubscribe rates suggest list fatigue or irrelevant content. Monitor this to understand subscriber satisfaction.
• Blocklist status (IP and domain): Regularly check if your sending IPs or domains are listed on any major public or private blocklists. Being listed is a strong indicator of deliverability issues. As mentioned, Mailtrap offers Free IP Blacklist Checker and Free Domain Blacklist Checker.
• Authentication failure rates (SPF, DKIM, DMARC): Monitor DMARC reports for authentication failures. A high number of failures suggests misconfigurations or, more seriously, unauthorized use of your domain (spoofing).
• ISP-specific feedback (Google Postmaster Tools, Microsoft SNDS): These invaluable tools provide direct insights from major mailbox providers on your domain and IP reputation, spam rates, and authentication errors specific to their ecosystems. Regularly check these dashboards for any warnings or changes in your sender health.

Utilizing monitoring tools for insight

For high-volume senders, manual checks aren’t enough. You need comprehensive tools that offer detailed analytics and actionable insights.

• Mailtrap’s deliverability analytics: As an email sending platform, Mailtrap provides in-depth analytics that are crucial for monitoring your deliverability. Our dashboard allows you to:
  • Track key sending metrics over time, including delivery rates, open rates, click rates, and bounce rates.
  • Monitor ISP engagement and performance across different mailbox providers.
  • Identify potential issues with detailed logs and reports that show why emails might be bouncing or failing authentication.
  • Gain visibility into DMARC reports, helping you identify authentication alignment issues or detect unauthorized sending from your domain.
  • Email spam checkers: Before sending critical campaigns, use a tool like Mailtrap’s Email Spam Checker to assess your email’s likelihood of being flagged as spam by various filters. This proactive check can save you from widespread delivery failures.

Further reading: How to Test Email Deliverability & What Tools to Use [2025] 

Proactive actions based on monitoring data

Monitoring is only half the battle; the other half is acting on the data.

• Analyze bounce logs and FBL data: Regularly review detailed bounce logs to understand the specific reasons for delivery failures. Combine this with FBL (Feedback Loop) data to identify and promptly remove complainers from your list.
  
  Note: Some ISPs won’t readily share FBL data for security reasons, so your best bet is using tools like Postmaster, SNDS, and similar. 

• Interpret DMARC reports for alignment issues: DMARC reports provide vital information on emails failing SPF or DKIM authentication and whether they’re aligned with your domain. Analyze these reports to fix misconfigurations or detect spoofing attempts.
• Regular sender reputation audits: Conduct periodic audits of your sender reputation, utilizing all available tools and data. 

Mastering the inbox: trust deliverability

Congrats! Together, we’ve walked through the intricate world of email deliverability, from the foundational technical configurations to the nuanced art of user engagement. 

For high-volume email senders and the software engineers supporting them, mastering these elements is not merely about avoiding the spam folder; it’s about ensuring your critical communications reach their intended recipients, fostering trust, and driving tangible business outcomes.

And remember, email deliverability is a marathon, not a sprint; a continuous cycle of implementation, monitoring, analysis, and adaptation.

With diligence, commitment to best practices, and the right tools at your disposal, you can build and maintain the sender reputation needed to earn the inbox’s trust, ensuring your messages always hit their mark.