Marketing & Communications
April 6, 2026

Recipe: Split Test Subject Lines to improve Email Open Rates

Recipe: Split Test Subject Lines to improve Email Open Rates
# Emails
# Marketing
# Recipes for success

Learn more about what your audience actually wants to read by split testing your subject lines. You can then use the data to make decisions which drive engagement

Recipe: Split Test Subject Lines to improve Email Open Rates
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What you need:

  • Access to build email campaigns in Dotdigital
  • An email campaign that is ready to send
  • Two subject lines 
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Time required

Prep time: 5 minutes 
Cook time: 2–4 hours (automated testing window)
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What will this help me achieve?

By pitting two subject lines against each other, you can let your audience’s real-time behaviour determine which version gets sent to the bulk of your mailing list. In the future, you can use what you learn about your audience to create content that drives engagement.
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Concepts we'll be using

  • Split Test: Also known as an A/B test. Measures the performance of two variables in your email to see which works best for your audience.
  • Clicks: a metric measuring the total number of times users interact with a button, link or content piece by clicking it, signifying direct engagement.
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Prep

Split test settings are configured on the campaign details page when setting up a new email in Dotdigital.
  • Select SPLIT TEST SETTINGS and ENABLE subject line:
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  • Above the campaign details, you will have Version A and Version B:
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  • Set a different subject line for both versions.

Activate

Create a new integrated email in Spektrix. When you select your email campaign, you will be presented with options for the test:
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  • Test percentage is the percentage of contacts to be included in the test. If the test percentage is set to 50%, then 25% will get version A and 25% will get version B of the campaign. The remaining 50% of your selected audience are sent the winning version once the testing period is finished.
  • The test period is how long the test will run, in hours.
  • The test metric is how the winner of the split test is determined. Choose clicks.
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More to explore

After the winning version has finished sending, check the  Email Campaign Report  in Dotdigital to see which subject line won. Consider what qualities the winning subject line had. For example, did it have a specific tone or CTA? Did it include a sense of urgency or an emoji? Use these insights to write even better subject lines next time. 
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