Testing email functionality with different clients

Testing your email functionality is critical to setting up any email campaign, but what happens when you switch email clients or use multiple tools to get more information? This article will review the email testing tools integrated into some of the most popular email clients you might use so you’re prepared for any situation.

Why conduct functional testing for emails?

Whenever you plan to send emails to many different addresses, it’s important to remember how your recipients will see the email. Recipients can use a variety of email clients, browsers, accessibility options, and operating systems, all of which have different rules they follow when interpreting and displaying the code that makes up the email you sent. Because of this, your emails might have bugs or other problems that don’t appear when you look at them in your inbox.
Testing how all those combinations interpret your emails is the only way to know. One way to do this involves sending test emails to a range of software combinations that your recipients are likely to use. Another way is through checking email preview tools build into the service you use to send your emails if there are any.

What mistakes to look for when checking your emails

What errors and bugs you’re likely to run into depends on the kinds of emails you’re sending, the email client you’re using, and what clients and other software your recipients are using. As you gain more experience with email testing, you’ll understand which mistakes are the most common and can adjust your testing strategies to prioritise finding them.

Here are some common errors to keep an eye out for:

  • Spelling and grammar mistakes
  • Formatting problems
  • Problems with images
  • Emails getting marked as spam

What types of testing does email marketing software have available?

Many popular kinds of email marketing software have some basic email testing capabilities built into their offerings, either for free or as an additional service added to your plan. Their tools usually fall into the following categories: email previews and sending test emails.

Email preview tools

Email preview tools give you an idea of what your email will look like in someone’s inbox, although they’re usually limited to showing a simple preview. They’re great for checking your email for spelling and grammar mistakes and checking that your links are correct. In order to effectively test your emails, you’ll need to run more thorough tests under some of the different conditions mentioned earlier.

Sending test emails

Many software suites will have a function to send a test email to a small number of addresses before sending out your entire campaign. This lets you check what your email will look like under a handful of different conditions and is also an excellent tool for sending previews to other people on your team and getting their feedback.

4 popular email marketing software companies and their built-in testing tools

Most email marketing software systems will have a way to preview your HTML emails, and many have options for sending a few test emails. We’ll review some of the most popular options and how to preview emails with their software.


Hubspot is a big name in digital marketing and email campaigns, partly because they offer many free courses and certifications in related topics. They also offer a vast array of software tools for sales and marketing, including email campaign management. Their software includes a drag-and-drop email template editor, which lets you preview what your email will look like as you build it. They also have a built-in more in-depth email previewing tool, showing what your email will look like depending on your browser and email client options. This makes HubSpot’s email marketing software a solid choice for people with limited testing needs.


Mailchimp is another popular choice for email marketing solutions, especially for people who use a lot of automation to send emails to groups of people when certain conditions are met. Like HubSpot, they offer an HTML email template editor, so creating well-designed emails is easy. They also have an email preview tool, although it requires a paid subscription, and all test emails count as part of the allowed monthly cap for your plan tier.


Another company that offers a solution for email marketing software is MooSend. In addition to the usual services like segmentation and A/B testing, Moosend has high-quality templates for desktop and mobile views to work with to make crafting great emails more straightforward and faster. The email editor will show what your email is supposed to look like, but you’ll need additional email testing tools to run previews and test different clients.

Constant Contact

Constant Contact has several tools designed to help you with digital marketing, including email marketing software. They have a lot of similar offerings as the others on this list, including drag-and-drop email template editors, lots of templates to choose from, analytics, and the ability to preview and send test emails. Their email preview tool is built into the editor & offers the option to look over your email in both a desktop and mobile layout. Their preview allows you to check to see what the email will look like to any of your specific contacts. All you have to do is put in the contact's email address, which will generate a preview of what your email will look like with the browser and client they use. You can also send out test versions to other people on your team.

More helpful tools for testing and improving your emails

Many companies offering email marketing software also provide free tools to help you improve and test your emails. You can often find them on their websites, either listed under tools or sometimes under products or resources. Some of these tools are featured below:

Copy and paste HTML email previewer

Mailninja offers a free HTML email preview tool that you can use to see how your HTML emails will look. All you have to do is copy and paste the HTML into the tool, and it will give you an instant preview along with the ability to toggle images on and off, check the email dimensions in pixels, and switch between desktop and mobile views.

Improve your subject lines

Moosend has developed a free tool to provide feedback and suggestions on improving your email's subject line based on the industry and the number of email subscribers you have.

Generate email signatures with social links

Hubspot has several free tools related to digital marketing and sales, including a small tool to help you generate a professional email signature with formatting, social links, and the option to add a small photo. There are several templates to choose from to find the one you like the best. They help add more professional emphasis to your emails.

Testing email functionality with Mailosaur

Most email marketing software can only preview and send test emails, and some have limitations on those features. For more in-depth testing, including automated testing, you’ll need additional software tools designed specifically for setting up your specialised email tests.

Mailosaur has developed software to help you check your emails for bugs that a glance over a preview won’t catch. Our software is used to create fake servers and unlimited email addresses and can be easily integrated with your favourite functional testing tools like Playground, Cypress, and Selenium so you can be sure your emails are putting your best foot forward, no matter how complex they are. Feel free to contact us with any questions, or try it free today!