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Create A/B test campaigns

Send two versions to a sample, let MailMachine pick the better one by clicks, and send the winner to the rest.

2 min read Updated 10 Jun 2026

A/B testing is an advanced feature available on selected plans. If you don't see A/B Tests in your account, it may not be included on your current plan - get in touch and we'll let you know your options.

An A/B test (or split test) sends two versions of a campaign to a sample of your list, sees which gets more clicks, and then sends the winner to everyone else - so MailMachine picks the better email for you. It's one of the most reliable ways to improve your results over time. This guide covers setting one up.

A/B testing needs a big enough sample to find a clear winner, since the decision is based on clicks. On a very small list, or a time-sensitive send, it may not reach a meaningful result in time - work out how long it'll take to gather enough clicks before you rely on it.

Set up an A/B test

  1. Click the Campaigns tab and select A/B Tests.
  2. Click the + to start a new test.
  3. Name it, choose a list and segment, and click Continue.
  4. Select the test block to open its distribution settings on the left:
    • By default, A and B are split 50/50.
    • Set the test distribution size and the winner size. For example, with a 40% test size and a 60% winner size, 40% of contacts receive the A/B sample and the better-performing version then goes to the remaining 60%.
  5. Set the winner criteria: when the test ends, and a fallback email to send if no clear winner emerges (when there isn't enough of a difference to be statistically meaningful).
  6. Select the Email A block, click Edit, and build it.
  7. To reuse A's content as a starting point for B, click Copy Email A Content to B, then vary it.
  8. Click Save and Exit, and do the same for Email B.
  9. When you're happy, click Start Test at the top right.

Your test runs, and you'll find it in your A/B test drafts to analyse. You can rename, delete or duplicate it from the arrow menu.

Troubleshooting

A/B testing isn't available - check it's included on your plan, and that your list is big enough to be meaningful.

Results are inconclusive - increase the sample size (around 1,000+ contacts is a sensible minimum), extend the test duration, and make sure your two versions are different enough to tell apart.

Winner-selection issues - review your criteria, always set a fallback email, and allow several hours for engagement to accumulate.

Distribution problems - make sure your test and winner percentages add up sensibly, and that your segments don't overlap.

For pre-send checks, see Testing your campaign. Stuck? Open a support ticket.

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