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Email Testing Checklist

On July 08, 2019
14min read
Yevgen Tsvetukhin Product Manager @Mailtrap

Email campaigns are an essential way to build trusting relationships with your digital project’s users. The idea is to provide valuable information to a number of recipients at once. And a tiny flaw can spoil all your efforts. A bad layout, a low inbox rate or simply kludgy content of your email can be the cause of a failure. But, you can avoid these troubles if using proper email testing tools. 

Unfortunately, you can’t use a single tool to check whether your email is ready-to-go. Though there are some large-scale solutions like Mailtrap or Litmus, you’ll likely have to opt for different options to do different testing. The main question is what exactly to test for your email campaign. We blogged about it in How to Test Emails in Mandrill, Sendgrid, and Mailgun. Here, you’ll find a universal email testing checklist for developers. It consists of three pillars:

  • testing of email sending capability  (SMTP server capabilities testing + test emails sending)
  • spam testing
  • email content testing 

Today, we’re going to inspect them from a hands-on standpoint. It means you’ll get not only an overview of how to test email but also which specific tool can help you with that. 

TL;DR table of email testing checklist and tools 

*  Click the name to jump to a specific section

SMTP server capabilities testing

What to testTools to use 
– Email server testingWormly
Web Wiz
– Load testing of SMTP ServerApache JMeter
MultiMail 2.0

Test emails sending

What to testTools to use 
– Sending test email via SMTPMailtrap
– Test email via API using scriptsMailtrap
Mandrill (paid only)
Mailinator (paid only)
– Unique email address per inboxMailtrap
– Shared inbox for the dev teamMailtrap
– Load testing of your app email sendingMailtrap

Deliverability or spam testing

What to testTools to use 
– Deliverability testSendinblue
– Email spam test
Mail Tester
– Email address validity test

Test email content

What to testTools to use 
– Email client testing or preview testLitmus
Email on Acid
Email Preview Services
Campaign Monitor
– HTML test
HTML Email Check
Email Markup Tester by Google
– Test body copyGrammarly
Hemingway Editor
– Email A/B testing or split testingCampaign Monitor 
Active Campaign
– Subject line testingSend Check It
Subject Line
Email Subject Line Grader

From the outset, you need to check if your code works and emails are actually sent. At the same time, the mail server is not the only aspect you need to test. That’s why we split the testing of email sending capability into two subcategories:
– SMTP server capabilities testing
– Test email sending

They involve various types of tests like load testing of server and app sending, email testing via API, and others.

Start Testing Now

SMTP server capabilities testing

Here, you need to check the functionality of your SMTP server using specialized email server testing tools. For this, you can either test your mail server or do load testing.

Email server testing 


Wormly is a solution for server, website, and uptime monitoring. You can use it to test your SMTP server easily as well. The tool sends a test email directly to your mail server for troubleshooting. Along with email server testing Wormly offers other free diagnostic tools including pop3 mail test, FTP server testing, etc. For those with higher-level needs, several paid subscription plans are available.

Free trial: available

Pricing: from $25/month


  • HTTPS Secured Web Server testing
  • POP3 Mail Server testing
  • Remote Ping


This is a powerful Gmail-centered service for email marketing. SMTP Test Tool lets you check your connection to any SMTP server including Sendgrid and Mailgun. Also, GMass offers a bunch of useful features for email marketing like automatic follow-up emails, behavior-based campaigns, email list builder, etc.

Free trial: available

Pricing: from $8.95/month


  • GMass Chrome Extension
  • Email Analyzer
  • Inbox, Spam, or Promotions
  • Link checker

Web Wiz

Web Wiz is not a dedicated testing tool but a solar-powered web hosting provider. Nevertheless, you might find it useful for the enhanced verification of mail server functionality. For example, Web Wiz users can do an IPv4 or IPv6 mail test, check SSL/TLS Connection Encryption for a domain or email address, and others. The service offers a bunch of DNS, IP, network, and email tools for free. 

Free email testing tool


  • DNS report
  • IP address information
  • Ping tool
  • DNSBL/URIBL spam database lookup

Load testing of SMTP server

Load testing typically lets you determine the processing capacity of your SMTP server. For this, you can benefit from two solutions: Apache JMeter and MultiMail 2.0. Both are free tools to stress test SMTP servers. 

Apache JMeter is a Java app for load testing functional behavior and performance measuring. It allows you to simulate a heavy load on a server or a set of servers. So, you can analyze overall performance under different load types. Along with SMTP server stress test, JMeter can be used to test different things like TCP, FTP, SOAP / REST Webservices, etc.

MultiMail 2.0 is a dinosaur app to load test mail server. It starts multiple threads that send a large number of emails in parallel to a specified SMTP server. The drawback of this tool is that you have to download and then install it on your device. 

In addition to these mail testing tools, it is rather easy to perform SMTP load testing in PowerShell. In this article, you can learn more about it.

Test emails sending

Now, you can use a third-party or dummy SMTP server to send test emails. These types of tests do not require the use of your mail server and let you check the email sending function of your app.

You may ask “Why do I need a third-party server if I can use mine?” You can, but we do not recommend you do this. If something is wrong with your app, a fake SMTP server will identify this without any harm to you and your customers. And the cost of a mistake can be rather high.

Sending test email via SMTP

If you can do with a simple SMTP server that catches emails, MailCatcher will fit. It works with multi-part emails and shows mail instantly (if your browser supports WebSockets). As for the drawbacks, the interface and mail processing is very basic. Besides, you’ll need to install MailCatcher to run. More on this tool, read in our Introduction to MailCatcher. As an alternative, you can try MailHog that we’ve also blogged about.

If you need an enhanced functionality and a rich feature set, Mailtrap will do the job.

Try Mailtrap for Free

Email API testing

You can also test email functionality via API using scripts. This can be done with Mailtrap or using one of the following tools. 


We don’t have to introduce Mailchimp, do we? Well, Mandrill is an add-on for Mailchimp. It provides an email infrastructure service. Also, you can test webhooks and templates via the Mandrill API. 

Free trial: not available

Pricing: from $10/block per month


  • Webhooks testing
  • Split testing
  • Spam filter testing
  • Multiple templates per account


This tool for QA & Development Teams works with a number of languages (Ruby, Python, Node.js….) and test frameworks (Nightwatch.js, SoapUI….). Mailosaur also provides spam testing and versatile content checks like broken links, subject lines, and HTML errors.

Free trial: available

Pricing: from $24/month


  • Automated end-to-end testing
  • Vast integration support
  • HTML test
  • Spam test


Another end-to-end testing solution with API is called MailSlurp. It lets you test email functionality with real email addresses. Also, you can send/receive emails via REST. This tool might be a good supplement to your test-suite. 

Free trial: available

Pricing: from €39.00 (~$45)/month


  • Complete end-to-end testing
  • Support of numerous official SDK Libraries
  • Send/receive emails from ephemeral addresses via REST

Unique email address per inbox 

The idea of this testing feature is to have a dedicated or unique email address for each of your inboxes. Let’s say you want to send a blind carbon copy (BCC) of production emails to one particular inbox that your development team can access. A testing tool allows you to make sure email sending works and production emails look and work as they have to. Additionally, you can check that custom variables in emails work well. Mailtrap is pretty useful for this kind of testing. 

Do not confuse the unique email address per inbox with the unified inbox feature provided by some email clients. It is a different thing that lets you manage emails and contacts from different mail accounts in a single inbox.

Shared inbox for the development team

A capability to share an inbox with the development team is also helpful for testing your email functionality. Unfortunately, there are not so many tools to help with that. Mailtrap offers a bunch of features including the shared inbox for the team. Another option to consider is Mailinator. This is a unique receive-only email system to test email workflow. With Mailinator, you can get multiple temporary shareable inboxes easily. A special feature, Super Inbox, provides subscribers with a dedicated private inbox, where you can see all emails in all the inboxes. The tool is free for personal use. Teams will have to pay from 159/month for extended features.

Load testing of your app email sending

Another check you might be willing to perform is to load test your app email sending. This refers to the number and speed of messages delivery. For example, you’re going to send 3K emails. What you need to test is how many messages will land into the inboxes and how fast will it happen. So far, this feature is not very widespread. Mailtrap provides it as Sending rate limits per 10 sec. Unfortunately, we failed to find any alternatives, so contact us if you find some.

Hopefully, this toolset is enough for you to check the functionality of your mail server. The next step would be to make sure that your email campaign won’t be marked as spam.

Deliverability or spam testing

Just a tiny reminder to the difference between delivery and deliverability. Delivery denotes whether your email campaign was accepted by a receiver or not. Deliverability indicates where the email ended up after delivery: inbox or spam folder. More on this, read in Email Deliverability Best Practices and Tricks. Now, meet the following set of email testing software.

Deliverability test 


This is a marketing suite for small and medium-sized businesses. With Sendinblue, you can manage email campaigns, send text messages, and do other digital marketing stuff. And, of course, this tool can be used to test the deliverability of emails. Testing includes two steps: sending a test campaign to a list of contacts and performing an inbox test. Once it’s done, you might be willing to try other Sendinblue features like Segmentation or Transactional Email.

Free trial: available

Pricing: from €19 (~$22)/month


  • Marketing automation
  • Signup forms
  • Email heat map
  • A/B testing


This is a hefty email service for developers. Mailgun provides a rather sophisticated mail deliverability test and offers a few solutions to improve the deliverability rate. These are email authentication, email address verification, and others. You can also opt for managed deliverability services. They provide customized strategy, custom reverse DNS, dedicated IP subnets, and so on.

Free trial: available

Pricing: from $4/month 


  • Email parsing
  • Transactional emails
  • Email validation
  • Burst sending


This service claims to be the most advanced email deliverability testing tool. SendForensics provides both pre-send and post-send optimization activities. It tailors a predictive model of how an email will reach recipients. With SendForensics, you get such features as email client preview testing, blacklist monitoring, content analysis, etc. 

Free trial: available

Pricing: from $49/month 


  • Enterprise Sender Assurance
  • Live Inbox Placement Testing
  • Deliverability Alerts
  • DMARC Compliance Verification

Email spam test 

Why emails going to spam? Read our blog post, and you’ll know how to avoid it. Also, you can send spam test emails with one of the mentioned tools: Mailgun, Mailosaur, and Mandrill. Mailtrap provides email and domain forwarding verification, as well as cross-databases spam checking. If these options, however, are no-go, consider the following ones.

Mail Tester

Mail Tester is probably one of the easiest-to-use email testers you’ve ever known. All you need to do is to send an email to a randomly generated email address shown on the main page. After that, push the “Then Check Your Score” button. You’ll get a detailed report of what’s configured properly and what’s not. The goal is to achieve a perfect score of 10/10. 

Free trial: available

Pricing: from €50 per 500 tests 


  • iFrame CSS and a JSON API to integrate results into customer software
  • Micro-payment mode 
  • 18 languages support


This is a specialized email tool tester to help you diagnose email deliverability problems. GlockApps allows you to check the reputation of your IP address or domain name, and run automatic tests regularly. It’s not as simple as Mail Tester but provides a wider toolset to maximize inbox deliverability.

Free trial: available

Pricing: from $25 per 100 spam tests 


  • Reputation monitor
  • Developer API
  • Gmail tab tracking
  • Automatic tests for outreach or transactional emails generates an individual email address that you can send your next email campaign to. A few seconds later, it will generate a report, listing all the issues with the content of your emails, your domain, infrastructure, and many others. It will also preview your message and suggest improvements.

Free trial: free forever with up to 10 tests and previews per month

Pricing: from $14/month 


  • Accessibility check
  • Email preview
  • Eye-tracking prediction heat map

Spam checker by Postmark

Postmark is an email delivery service. It provides really cool features like Postmark Status showing the time-to-inbox of your messages. As for the spam score check, you can do it for free by pasting the entire text of your email. Moreover, the message will be verified according to the SpamAssassin score – the most widely used spam filter.  

Free trial: available

Pricing: from $10/month 


  • JSON API to integrate spam score processing in your software
  • Postmark delivery status 
  • Versatile email sending options

Email address validity test 

There are a bunch of free email testing options to verify whether a particular email address exists or not. But you’ll have to pay for bulk email validation anyway. An email campaign might require thousands or hundreds of thousands of addresses to be validated. Here are the options you can benefit from.


According to G2, TheChecker is the number one tool to test email address validity. Besides, it is one of the most cost-effective solutions on the market. The tool provides multilingual customer support and offers custom plans to fit specific needs of its clients. As for the processing speed, 100K email addresses verifications take less than one hour. 

Free trial: available

Pricing: from $3 per 1K email addresses 


  • 99% validation accuracy 
  • Powerful API
  • TXT, CSV, XLS & XLSX formats supported
  • Free email duplication removal


This email tester promises 96% deliverability for affordable pricing. When we were writing this article, MyEmailVerifier was running a super saver 40% discount program. Compared to TheChecker, this service supports only TXT and CSV formats. But the turnaround time is faster: it only takes 45 minutes to validate 100K emails addresses. 

Free trial: available

Pricing: from $̶4̶.̶8 2.88 per 1K email addresses


  • Real-time verification through API
  • High risk email detection
  • Syntax verifier
  • Detectors: Temporary Unavailability, Catch-all, Rola Account


Do not confuse this service with one of the email validation flagships – ZeroBounce. At the same time, NeverBounce is also a noticeable tool being used by Uber, Dell, and Indeed. The service offers an extremely fast turnaround time – 45 minutes for 100K email addresses and less than 10 minutes for 10K. Also, you can connect NeverBounce with almost 90 famous tools like Salesforce or SendGrid. And, of course, the deliverability rate is 99%. 

Free trial: available

Pricing: from $8 per 1K email addresses


  • Flexible pricing options
  • Mail Server Validation
  • Domain Health Check
  • Custom API and Webhook

Truth be told, the list of email address validators is endless. Those above are well-balanced as for accuracy, speed, and pricing. Other noteworthy tools include ClearOut, Bouncer, and many more.

Test mail content

That’s it! The third pillar of our universal checklist on how to test email sending. Here, we’ll focus on tools that help you check text and formatting, as well as dynamic content of emails. Also, we’ll review A/B tests capabilities for email campaigns. 

Email client testing or email preview

Client testing is checking how an email looks at different devices, browsers, or email clients. Most dedicated tools use the Email Preview term to denote this functionality. Also, you can encounter Browserstack Email Testing. Despite these variations in namings, the gist is the same – to look at the email from different perspectives. And here are the best options to do this kind of testing.


The first thing you need to know about Litmus is that your email will be previewed across over 90 apps and devices. These include Desktop clients like Outlook and Apple Mail, multiple mobile apps, and the most widespread web clients. Litmus is a powerful solution to build, test, and monitor email campaigns. Along with email preview, you can benefit from spam testing, email analytics, and other valuable features. 

Free trial: available

Pricing: from $99/month 


  • Spam testing
  • Litmus builder
  • Advanced Security
  • Integrations with famous marketing tools 

Email on Acid

Email on Acid also provides a long list of mobile, web, and desktop clients that your email will be previewed on. With this tool, as they promise, your email life will be a little easier. Also, EoA will verify every link in your email and assist in finding the best code solutions in the test result window.

Free trial: available

Pricing: from $55/month ($44/month if you pay annually)


  • HTML testing
  • URL validation
  • B2B/B2C spam filter testing 
  • Heat mapping

Email Preview Services

Email Preview Services is a cutting edge solution to test email design. It provides you with screenshots of real device experience on most popular email apps, so you can tweak your content if necessary. Similarly to Litmus and EoA, this tool covers desktop, web, and mobile email clients. Apart from preview testing, Email Preview Services provides inbox and spam testing as well. 

Free trial: available

Pricing: from $25/month


  • 100% White-Label API
  • Spam Score Testing
  • Delivery Duration Tracking
  • Email Analytics

You can enhance this list with other tools. Mailchimp, Campaign Monitor also provide email preview testing capabilities.

HTML test 

HTML test is a sort of email preview, but with the emphasis made at the markup (HTML, XHTML, and CSS) validation of your email campaign. Such services as Mailgun or Mailtrap provide this functionality out-of-the-box. If you’re interested in a separate HTML tester, here is what you can choose from.


Originally, the tool was developed by Pablo Cantero and went under the wing of Litmus in 2014. PutsMail is an HTML validator with a capability to inline CSS. The test procedure is rather simple and consists of three steps:

  • Add recipients (up to 10 email addresses)
  • Add a subject line
  • Add a body in the form of HTML, plain text, or text for Apple Watch users.

PutsMail also keeps a list of previous tests. And all that is for free. 

Free tool


  • CSS inliner
  • Test history

HTML Email Check

With HTML Email Check, you get a set of tools to validate HTML markup, CSS formatting, client-specific styling, and many more. Also, the service offers a free HTML email template responsive for both desktop and mobile apps. 

Free test: available

Pricing: $14.95/month for HTML Email Check PRO


  • Accessibility validation
  • Layout viewer
  • Mobile validation
  • Developer Checklist

Other tools 

As the third option, we brought together a few HTML checkers that are rather simple-in-use and alike. Email Markup Tester by Google is a field to insert HTML source of your email and a Validate button. Accessible-email has an interesting interface and lets you analyze the sent campaigns. You can also consider PilotMail, it has promising functionality with such features as multi-part email testing, CSS auto inline, and others.

Test email body copy

Now, let’s brush up the body copy of your email. The following tools will help you eliminate typos and grammar mistakes. Also, they are useful to increase the readability of your email campaign.


This tool is a noteworthy writing assistant. Grammarly not only points out when you’ve missed an article but also detects over 400 types of grammatical mistakes. It is available as a web app, desktop app, and a Chrome/Safari/Firefox extension.

Free trial: available

Pricing: from $11.66/month (if you pay annually)


  • Grammar checks
  • Punctuation checks
  • Sentence structure checks
  • Plagiarism detector

Hemingway Editor

The lines above, below and those you’re reading now have been checked with this tool. Hemingway Editor allows you to improve the readability of texts. It detects hard-to-read sentences and other complex structures. Also, it has a built-in counter of letters, words, and even reading time. For this paragraph, we got a readability score of 6, which is good:)

Free tool


  • Readability check
  • Counter of letters, characters, words, sentences, paragraphs 
  • Reading time counter


Plagiarism checking is mostly SEO stuff. But if you don’t want your recipients to think “Oh, I’ve read that before somewhere”, make sure that your body copy is plagiarism free. Unicheck is a powerful checker trusted by hundreds of Academic Institutions around the world. 

Free trial: up to 200 words

Pricing: from $5 per 20 pages


  • Personal dashboard
  • API
  • Google Docs add-on

Email split testing or A/B testing

Email A/B testing denotes that a small number of total recipients get two different variations (A and B) of the email campaign. The variation with the highest rate of opens and clicks goes to production. You can split test your emails manually, but the following tools have a built-in functionality for that. 


Email A/B testing with Mailchimp looks as follows. First, you pick the audience you want to send your campaign to. Then, choose elements to test: subject line, content, send time. Also, you can use up to 3 variations of elements under testing. In the end, you need to specify the percentage of recipients and criteria to determine a winner. These are click rate, open rate, total revenue, or the manual option. Then, just set up the campaign and that’s it.

Free trial: available

Pricing: from $9.99/month


  • Custom-coded templates
  • Comparative reporting
  • Integrations with 200+ Apps
  • 24/7 Email & Chat Support

Campaign Monitor 

The email split testing procedure in Campaign Monitor looks similar. You can read about it here. What you might like about this tool is the results monitor. It is a graph that shows you your campaign is doing. Results are defined according to the chosen performance metric: open rate, total unique clicks, or total clicks. Also, you can manually pick the winner if necessary.

Free trial: you can set up an account and create a campaign for free. But you need a subscription plan to send the campaign to more than 5 recipients

Pricing: from $9/month


  • Hundreds of professionally-designed templates.
  • Visual journey designer
  • Sign-up forms
  • Vast analytical capabilities 

Active Campaign

Active Campaign promises to make split testing as easy as launching an email campaign. The tool lets you test content, subject lines, from name, images, and CTA. Actually, Active Campaign doesn’t provide A/B testing, but rather A/B/C/D/E testing, and that’s awesome! And of course, the way the tool visualizes the results is enjoyable and informative. 

Free trial: available

Pricing: from $9/month


  • Free and fast migration option
  • Dynamic content
  • Subscription forms
  • Email segmentation 

Subject line testing 

With so many tests already done, why do we need to check the subject line separately? That’s a reasonable question with a definite answer – the subject line is a core trigger for open rate. Therefore, we do recommend you pre-test your subject lines before sending your email campaign.

Send Check It:

Meet a reliable and easy-to-use subject line checker. As useful features, Send Check It provides a Slack Subject Line Tester and API. You’re unlikely to need anything else. 

Subject Line

Subject Line works fast and gives exactly what you need to understand whether your subject line is a go or no go. Just paste your text in the field and hit Evaluate. Your target score is 100. Give it a try! 

Email Subject Line Grader

This checker by Net Atlantic is also no frills. Email Subject Line Grader not only sets a grade to your subject line but also explains what’s wrong with it. For example, here is the tip we’ve got from this tool: This email subject line could be improved with some words with emotion, action, or power.

Wrapping Up

Congrats, you’ve made it to the end of our email testing tools list. Now, you’re armed with useful tools and services to make this process fast and smooth. Also, remember that new tools are appearing on the market all the time, which you should not hesitate to try. They might give the unique value you’re looking for.

Article by Yevgen Tsvetukhin Product Manager @Mailtrap