HTML e-mail has come along way but different e-mail clients still load and display HTML emails different. The best way to reduce risk of someone seeing a poorly formatted e-mail is to test them in a tool that can show you how your e-mail will render multiple e-mail clients.
The test tool works by loading and rendering the e-mail and sending you a screenshot of the presentation. This ensure that the email will appear exactly as the user will receive it.
Most of the time problems come froma version of Microsoft Outlook, which is often use by business customers but sometimes it’s an iPhone E-mail issue which effects most mobile users. You can review and decide if you want to adjust your HTML email to appear better.
If you’re getting started and looking for a cheaper option MailChimp includes and Inbox Preview tool that is $3 for 25 test tokens. This means you can test your email 25 times for $3, which is great value. The process is best used when your using MailChimp but you could design your HTML email in MailChimp and then use another tool for the final delivery.
If you have multiple people working on different e-mails using MailChimp alone can become cumbersome and a specific service to test e-mails can be a benefit. Some of the most popular are:
https://litmus.com/
https://www.emailonacid.com/
http://www.emailreach.com/
http://previewmyemail.com/
MailChimp Inbox Preview is based in the Litmus tool and it’s by far the most popular tool. All of the services provide a screenshot of your e-mail being rendered. Expect to see 50+ e-mails being render in hopefully the same HTML layout, most of the time it’s a smaller number of e-mail clients that you focus on and older clients like Lotus Notes can be safely ignored unless you have a particular need for the e-mail client.
Archiving prior tests, we often want to compare e-mails to make sure that a new template renders as well as a previous version. This is especially important with responsive HTML emails, having these tests easily available also helps the new team members understand how prior e-mails performed in testing.
Another component of e-mail testing is to look for issues that will trigger spam filters. This focus most on the content of the e-mail and looks for on spam filter trigger words that might be a problem. Generally a well written email shouldn’t have much issue with spam filters and you can monitor the open rate of your e-mails in your delivery service to catch and major content issues.
Many testing tools have extended their services to include e-mail analytics and measurement features. These are often a duplicate of features you already have if your using a email delivery service. As a result I don’t spend much time evaluating these.
Most of the services offer a evaluation period so you can experiment and see which works best for you and your team. It’s a good plan to use the evaluation period with a variety of different campaigns that focus on business or consumer e-mails as they often use different e-mail clients. I also like to test different languages as English and French e-mails can render different depending on the word breaks.
After evaluating the services above I think Litmus is still the best e-mail testing tool. It provides the best work flow and allows teams to review previous tests quickly. E-mail on Acid is the runner up but I think the interface and on-boarding process is a little behind Litmus.