Before you answer this question, let us clarify–are you testing your emails on an ongoing basis? There is no one and done methodology with email. Your customers are constantly evolving (and likely so is your product), so it’s imperative that you keep testing  different elements of your emails to ensure that you are sending the most optimized campaigns.

Email Testing Categories

When it comes to email testing, there are three main categories you need to cover – content, design and timing. Content consists of everything from subject lines, to headlines, to calls to action, and each have their own significance in driving response from your users.

Design testing has to do with the look and feel of your email, but has a primary focus on placement. Where your text and imagery live on your email template can affect response rates. Design testing incorporates everything from fonts, font size, formatting, and plain text vs. HTML.

Time testing helps you determine when you should send your emails. This refers to day of the week, time of day, frequency, and ultimately cadence. We often get asked about when the best time to send an email is—and frankly, it’s a question that we can’t accurately answer. Optimal times to increase open and click rates vary by industry and subscriber base, so the only way to really know the perfect time to send emails to your users is to test it.

Getting Started With Testing

Keep it simple and start small. First, determine your goals. Is it to increase open rates or clicks? While it might be both, choose one to start with and then select one element that would affect that outcome. For instance, subject lines are critical to open rates while calls to action are critical to driving clicks. As you test your subject lines or CTAs, be sure that you’re sending your tests at the same time of day to eliminate that as a variable (unless you are testing time of day of course).

To learn more about A/B testing the content, design, and timing of your email, download our latest guide, Why A/B Testing is Critical to Email Campaign Success.


As Twilio SendGrid's Sr. Director of Content, Jillian is responsible for ensuring that SendGrid provides valuable thought leadership content through the blog, whitepapers, webcasts, and more. When not writing and editing, you can find Jillian frequenting Denver restaurants in search of the best queso.