The Complete Guide To Email Testing

With an unmatched ROI, email is still the most effective marketing channel to invest in. When done right, it can have a significant impact on your bottom line. That’s why it’s so important to make sure you’re sending emails that work. If you’re not working on optimizing your emails yet, you’re basically leaving money on the table.

You always want to be certain that your emails perform the best they can. Luckily, email testing can help you catch any errors before you hit “send.”

In this article, we’ll discuss why email testing is so important, what the most common problems with emails are, and we’ll even show you the most popular tools for testing. Let’s get to it.

Why you need email testing

You’ve spent hours crafting a new email campaign for your business. You’ve selected the best template, carefully crafted a subject line and agonized over every word in your CTA, all with the hope to get high open and click-through rates that will bring in new sales.

All this effort could have been for nothing if your email doesn’t even make it into your subscriber’s inboxes. Or worse, it does, but with broken links, images that don’t show or a weird typeface. Blunders like these can cost you more than just subscribers. They can stain your credibility as a business by making you look unprofessional.

Right now, there are 50+ email client and device combinations on which your subscribers could be opening your emails. (In case you’re curious, here are the most popular email clients.) 53% of all emails are opened on mobile devices. That leaves a lot of room for errors when you’re emails are not optimized to work across different email clients.

To complicate this even more, email clients constantly update their software. That means a template that worked one month could have problems in the next. The support for your HTML/CSS features could have changed resulting in issues that you didn’t originally have before.

Without regular email testing, you run the risk of sending emails that could potentially alienate your subscribers, cost you new business, and waste your marketing dollars. We firmly believe that the high potential for a solid ROI on your emails makes it worth to invest in rigorous testing.

The most common problems with emails

Email performance is complex, but most problems occur in three areas: deliverability, opens, and viewing experience & clickthrough. Each one has its own set of challenges. We’re here to help you navigate them confidently.


You want your email to directly reach your subscriber’s inbox, and not get stuck in the spam folder. Spam filter algorithms are always shifting and even as a legitimate sender you might get caught in them. Read our tips to find out if your emails are going to junk.)

The main reason for your emails being filtered or blocked is likely a low sender reputation. ISPs even tend to reject emails that fall below a certain sender score automatically. So, if you’re wondering what could hurt your sender reputation, here are the main factors:

  • Spam complaints by your subscribers
  • IP address or domain on a blacklist
  • Low engagement (for example, open rates)
  • Inconsistent frequency in sending emails
  • Fluctuating list size

What could you do right now to improve your deliverability? We’ve compiled four tests that you can run to ensure that your emails make it into your subscribers’ inboxes and won’t be flagged as spam:

  1. Check your email list for invalid email addresses and remove them regularly. There are several services that allow you to check emails for validity.
  2. Check your email list for spam traps and remove them from your list.
  3. Check your IP and sender reputation to make sure they aren’t flagged.
  4. Check your emails for spammy words in subject lines and email content.


Once your email has reached your subscriber’s inbox, you want them to open it, of course. Your subject line and the “from” email address have the biggest influence on that. (Check out our 5 tips for writing better subject lines.)

Here are the common problems that’ll prevent subscribers from opening your emails:

  • The subject line is too short or too long.
  • The subject line seems like clickbait.
  • The subject line is unengaging and boring.
  • It’s unclear what the email is about.
  • The “From” is a generic email address like

Viewing experience & click-through

Having your email opened gets you one step closer to your goal. At this point, you want to be sure that your email is displayed correctly and subscribers can’t wait to click your CTA. Your email template and the way you structure your email play an important role here.

Here are the common problems that can prevent subscribers from taking action:

  • Broken Links
  • Template not showing correctly
  • Missing image ALT text for email clients which block images
  • Blurry images
  • Font not showing correctly
  • Missing tagging in links
  • Text CTAs being too hard to click on mobile devices

The most popular tools for email testing

There are plenty of options out there that can help you test for the various problems in emails. But your time is limited, and you probably don’t want to jump between several different tools to get the job done. That’s why we prefer tools that test as much as possible at once.

Check out our recommendations below. We’ll also mention some specialized tools that let you test a particular aspect of your emails.


Litmus is probably the biggest name in the email testing space. They provide a comprehensive toolset that includes the following features. If you’re curious to try it out, Litmus offers a 7-day free trial.

  • Previews your emails across 90+ email clients.
  • Analyzes email performance and fine-tunes your campaigns for the best results.
  • Spam tests your email to identify potential issues before sending.
  • Guided QA to test all critical elements of your email.
  • Streamlines internal email reviews and approval.
  • Integrates seamlessly with most ESPs.

Email on Acid

Email on Acid offers a great deal of the features that Litmus does. They also have a 7-day free trial. If you’re looking for an email testing tool that can integrate into your own platform, then Email on Acid’s White Label Solution might be the right one for you.

  • Tests your email across 70+ email clients and devices.
  • Tracks and analyzes email performance.
  • Spam tests your email to find any problems.
  • Lets you build, edit, and optimize your email right in the platform.
  • Offers a library of email templates.

Subject Line

Your subject line is critical to get people to open your email. Litmus has a basic subject line checker that will let you preview your subject line in the different email clients. However, it won’t show you how effective it is in getting your email opened.

That’s where our tool Best Subject Line comes in! It takes into consideration the best practices that we have identified after analyzing countless email campaigns. Simply enter your subject line and run the analysis. Your subject line will be scored according to its length, the combination of words, numbers, and emojis, its sentiment and the type. As a result, you’ll receive specific suggestions on how to improve your subject line for a maximum open rate.

Other email preview tools

If you’re simply looking for a tool that lets you preview your email in different email clients, you can check out the ones below:

Other spam testing and sender reputation tools

If you’re just looking for a tool that can help you with your email deliverability, you can check out the ones below:

Send Forensics – free

It’s your turn

Now that you have a solid knowledge of email testing, you can start implementing it for your business. Remember, it could take only one broken email to hurt your business’s reputation. The earlier you start testing your emails, the faster you can optimize them for better conversions that’ll increase your email marketing ROI.

If email testing still seems like a daunting task to you, why not let our email marketing experts take care of it? We can completely manage your email campaigns and get the results you’re looking for – without you lifting a finger. Let’s get in touch!