A/B testing involves sending two different versions of an email to a small portion of your list to see which one performs better. Here are some elements you can test: 1. Subject lines: Test different subject lines to see which one has a higher open rate. 2. Email Content: Test different layouts, images, and CTAs to see which one drives more engagement. 3. Send Times: Test sending emails at different times of the day or week to see when your audience is most responsive.