What is the best way to A/B test email subject lines for maximum open rates?

All answers to this question.

Consistency comes from testing one variable at a time. If you test "Emoji" vs "No Emoji," keep the text identical. For sample size, most ESPs recommend a 20/20/60 split: send Version A to 20% of your list, Version B to 20%, and then the winner to the remaining 60% after 4 hours. In tech, "Curiosity" often beats "Urgency." Instead of "Last Chance for 20% Off," try "A quick question about your [Service] stack." This feels less like a promotion and more like an inquiry, which naturally piques interest in a crowded inbox.

   Answered 2025-06-10 by Deborah Lewis

Do you also track the "Click-to-Open Rate" (CTOR) for your winners, or are you only looking at the initial open rate to judge success?

   Answered 2025-06-25 by Jason Lee

• We haven't been looking at CTOR as closely as we should, Jason. Sometimes a "clickbait" subject line gets a huge open rate, but the actual clicks inside the email are lower because the content didn't match the hype. I’m going to start prioritizing the CTOR as the primary metric for our A/B tests to ensure we aren't just tricking people into opening an email they don't actually want.

     Commented 2025-07-05 by Thomas Wright

Personalizing the subject line with the recipient's "Company Name" is currently outperforming "First Name" in our B2B SaaS campaigns.

   Answered 2025-07-18 by Amanda White

• I agree with Amanda. It feels much more relevant to their professional daily life. We've seen a 5% lift just by making that one small change.

     Commented 2025-07-25 by Ryan Mitchell