email marketing testing tools illustration

What Email Testing Tools Do You Really Need in 2024? 

If you put your email program to the test, would it make the grade? The answer may depend on what types of email testing tools you use. We’ve previously explained how there are two types of email optimization testing. Turns out, we may have undercounted.

From signup to inbox placement and everything that happens in between, there’s plenty that can go haywire in the wild world of email. If you don’t put an end to these potential problems, they’ll reduce the email channel’s impact on your marketing efforts and the customer experience.

So, what does your company need to get the most out of email marketing? Let’s look at every type of email testing tool as well as when and why you’d want to use each one.

5 types of email testing tools

If you’re searching for the right email testing tool, you probably have a specific problem in mind. You may want to optimize emails for better performance, ensure HTML email campaigns display correctly, or test factors related to email deliverability.

Each one of these situations requires a different type of tool. Here are the five email testing software we’ll explain in this article:

  1. Email address validation
  2. HTML email previews
  3. Email quality assurance testing
  4. Email A/B testing
  5. Inbox placement/spam testing

Many of the popular tech review sites like G2 and TrustRadius lump these email testing tools together. It’s time to clear up the confusion so you can find the right fix.

1. Email address validation

Let’s start at the beginning of the email customer journey – the point of signup. That magical moment when a new subscriber decides it’s time to give you permission to email them. In many cases, they’ll opt in through a form on your website.

But what happens if they’re so excited to join your list (hey it could happen) that they accidentally type instead of There may also be people who just want to get their hands on that free download, and they use fake contact information or disposable email addresses.

Email testing tools that can help prevent bad contact data from landing on your list are known as email address validation or email verification tools.

An email validation service determines whether an address is real by testing to see if it can be reached. There are solutions that validate emails at signup as well as those that verify contacts on your entire list. That’s needed too – because people abandon personal email accounts, graduate from college, and change jobs leaving old addresses behind.

Why it’s important

Besides the obvious reason that sending messages to a non-existent contact is a waste, there are other important reasons to conduct email validation. The biggest relates to your sender reputation and deliverability.

Since there’s no one on the receiving end of an invalid email address, bad contact data could drag down your email engagement rates. Invalid emails also lead to high bounce rates, which is another factor that can hurt deliverability. Mailbox providers like Gmail, Yahoo, and Outlook take notice of low engagement and bounce rates.

Most dangerous of all are spam traps. Sometimes, abandoned email accounts are recycled to catch spammers. If you send to one of these recycled spam traps, mailbox providers may decide to filter your messages to junk or add you to a blocklist.

One way to avoid email verification pitfalls is to implement a double opt-in, which asks new contacts to confirm their intent to sign up. You don’t add them to your list unless they click the link in a confirmation email.

Who needs this type of email testing tool?

If you’re a bulk email sender with a list that is constantly growing with contact data from new customers and prospects, email validation is vital to good list hygiene.

Verifying new contacts at sign up helps keep your list clean, but you should also periodically check your entire list. One solution that lets senders do both is Mailgun Validate.

Mailgun Validate email test results

Using Mailgun’s Email Validation API, you can catch bad addresses in real time - before they get into your database. The tool can even identify common email address typos and suggest a fix. List Validation features let senders verify contact data in bulk. This is useful for regularly scheduled list hygiene or when you may be legimately adding a large number of new contacts.

Unlike other email testing tools for address verification, Mailgun Validate uses real cached send data as opposed to broken SMTP handshake. (Oh, and it’s also super-fast.)

2. HTML email previews

Once upon a time, there was a digital marketer who was blissfully unaware that whilst his emails looked great inside a popular ESP’s editor, they rendered like hot garbage in some of the most popular email clients. (This is a true story about me.)

Most email marketing software shows you how your campaign looks on mobile and desktop, but the real problems come with the way email clients render HTML and CSS. Email rendering differs depending on the inbox provider/client. To get the full picture, we always suggest visiting

Desktop versions of Outlook, for example, are particularly problematic. But Gmail and other providers have their issues too. Even though there’s a new Outlook coming in 2024 that will fix some issues, the old versions aren’t disappearing just yet.

Email previews are screenshots from inside of actual inboxes that show you how an HTML email campaign renders in different clients, devices, and operating systems. These previews help senders find and fix problems like random white lines in Outlook or rendering issues with dark mode emails.

Why it’s important

Brands want their email campaigns to reach inboxes looking as perfect as possible. When emails show up with broken layouts it reflects poorly on the brand. Sometimes the way campaigns are displayed makes emails unreadable. So, rendering inconsistencies can also reduce email engagement.

Who needs this type of email testing tool?

Senders with teams that include an in-house email developer who codes campaigns from scratch will almost always need this type of email testing. Email previews are also an essential test for digital agencies and freelancers specializing in email marketing.

Sinch Mailjet’s report, The path to email engagement 2024, found that 71.5% of global consumers check their inbox on a mobile device. So, emails must be responsive if you want them to look and function properly on smartphones. Mobile device previews help you catch those problems.

Testing mobile email clients

Email previews from Sinch Email on Acid include more than 100 of the most popular clients and live devices. That includes dark mode previews. Senders can tailor their email testing profiles for the inboxes that matter most.

There are only a couple players in the email preview game. We won’t mention our competitor, but their name rhymes with Spit-Bus. (Okay, it’s Litmus.) If you’re using a marketing platform that already provides email previews, there’s a good chance they’re using an API to white label one of our services.

3. Email quality assurance testing

Email quality assurance (QA) is a more all-encompassing way to test email campaigns. While rendering issues are one of the biggest challenges of email  development, there are many other things marketing teams should double-check before hitting the send button.

There are the little things like typos and accidental profanities (cuz shit happens). There are also bigger problems like broken links, email accessibility, and blocklists to worry about. Once your campaign reaches inboxes, there’s no taking things back.

Some teams use an email marketing checklist for quality assurance. The problem is, if this process is mostly manual, it leaves lots of room for human error. An automated checklist creates a consistent workflow for pre-send email testing that’s much more dependable.

Why it’s important

While email marketing delivers a high return on investment (ROI), your campaigns need to be optimized for every inbox and every subscriber if you want to get the most out of each campaign.

Customers can’t convert if broken links fail to take them to your landing pages. Accessibility issues could make text unreadable or mobile email CTA buttons untappable. Mistakes in an email marketing campaign do more than damage your brand reputation. Failure to conduct email quality assurance testing also ends up reducing revenue the email channel generates.

Who needs this type of email testing tool?

Whether you’re a recognizable brand or a smaller online store, if you rely on email to drum up business and drive customers to your website, you need to conduct pre-send testing for quality assurance.

Product illustration of accessibility email testing tool

At Sinch Email on Acid, our automated workflow is known as Campaign Precheck. It includes spell check, inbox display optimization, basic deliverability checks, accessibility fixes, and more. You can customize your quality assurance process however you want. Of course, you’ll also get unlimited testing including our reliable Email Previews.

Besides being a valuable email testing tool, Email on Acid also helps teams collaborate on review and approval of campaigns with Team Management features.

4. Email A/B testing

While email validation and previews are important tests before a campaign launches, there’s another type of testing that helps senders optimize for performance metrics such as opens and clicks.

Email A/B testing (aka split testing) lets marketing teams experiment with different campaign elements to discover what’s most effective. Subject line testing is just one of many experiments. You find out if subject line A gets a higher open rate than subject line B, for example. You could test CTA button placement, color, or copy. The imagery, headlines, messaging, and offers in your emails are also things to A/B test.

Why it’s important

The purpose of A/B testing is optimizing email design and copy in a way that resonates with your list so you drive email engagement. While you may have opinions about what will work, opinions can be wrong. Even so-called best practices may not be the approach that delivers the best results.

The only way to know for sure is to A/B test email campaigns. The winning variable will often surprise you. That’s why the marketing mantra “Always Be Testing” (ABT) exists.

Who needs this type of email testing tool?

Any email marketer who wants to improve campaign performance and gain a better understanding of their subscribers should take advantage of A/B testing.

Mailjet email A/B testing results

Many ESPs will include email testing tools like this as part of the platform. That includes Sinch Mailjet A/B testing, where you can define specific criteria for different tests depending on the metric you want to improve. With Mailjet, you can test up to 10 versions of an email campaign at once.

5. Inbox placement/spam testing

The fifth and final example on our list of email testing tools helps senders avoid one of the most dreaded destinations in all of digital marketing... the spam folder.

Inbox placement refers to your ability to reach recipients’ inboxes rather than being filtered into spam or rejected by receiving mail servers. Inbox placement may also be referred to as seed testing or spam testing tools.

The term “seed testing” is used because test emails are sent to a unique set of email addresses known as seed mailboxes. The seed list does not contain any real contacts. The addresses exist to generate a report on inbox placement. It shows the sender if a mailbox provider is likely to let a message reach the inbox, send it to spam, or block it altogether.

Besides just telling you where emails are likely to land, a good inbox placement report helps senders identify and fix specific deliverability issues. That includes problems with email headers, authentication protocols, and many other possibilities.

Why it’s important

New requirements from Gmail and Yahoo in 2024 have many senders paying closer attention to their deliverability. Sinch Mailgun’s report, Email and the customer experience 2024, found that more than 72% of consumers have a Gmail account while more than 20% use Yahoo Mail. So, if you want to reach people, you’ve got to follow the new requirements.

Understanding how these providers filter your emails helps you catch deliverability issues right away so they can be addressed. With the right inbox placement testing tool, you’ll get an accurate deliverability estimation before your emails go out to recipients.

Who needs this type of email testing tool?

Some emails are more important than others.  For example, if your business relies on transactional emails to keep customers satisfied and business running smoothly, then deliverability of those messages is crucial.

You don’t ever want transactional emails landing in spam. Promotional emails can be important too – especially at certain times of the year such as Black Friday and Cyber Monday.

Inbox Placement testing results

The truth is, deliverability is the most mysterious part of sending email, and inbox placement testing can demystify many things. The inbox placement reports from Mailgun Optimize are just one of the many useful tools you’ll find in a complete email deliverability suite.

Are there any free email testing tools?

The answer is yes – you will find some free versions of email testing tools around the web. However, the old adages “Buyer beware” and “You get what you pay for” definitely apply here.

For example, many free email validation tools only allow you to check one email at a time. Have fun with that. Free email testing tools that provide spam scores are also very limited. You can test a few emails before you get cut off, and who knows how reliable it is. Free HTML email previews usually provide a very limited number of tests and clients.

You’ll also find plenty of blog posts claiming to list free email testing tools, but they are really showing paid tools that offer free trials.  There’s absolutely nothing wrong with free trials, but if you care about quality and reliability, it’s worth investing in email testing tools you can trust.

Comprehensive email testing platforms

What if you want all the email testing tools? The good news is that some of the solutions we’ve mentioned in this article do provide more than one type of testing.

With Sinch Email on Acid, you get previews and a comprehensive email quality insurance platform that includes basic deliverability checks.

With Mailgun Optimize you get a complete email deliverability suite that includes both email validations and inbox placement tests as well as Email Previews powered by Email on Acid. There’s also blocklist monitoring to help manage your sender reputation and a Google Postmaster Tools integration.

Whether it’s performance optimization, deliverability, or rendering, email can get complicated in a hurry. Thankfully, the Sinch Email brands are here to help clear up confusion with email testing tools that put you on the right path.

Built for Busy Email Teams

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