Subject Line & Selecting

To use the subject line tester, create your message as normal and on the Message settings page, under the subject line options area there is an option to add another subject line

You will then notice another subject line text area appear under the original. You can now enter your second subject line. You can add up to a total of five subject lines.

Once you have more two or more subject lines and have entered the text into the fields, you will then be able to select one of two options, tester or selector.



Classic A/B test. Send each subject line to an equal split of your campaign recipients and analyse the results yourself after the campaign has finished sending.

Subject line selector

Subject line selector is only effective when over 10,000 emails are sent.

Subject Line Selector will test all of your subject lines on up to 5,000 records for an hour. If there is a clear winner at the end of the hour, that winning subject line will be sent to the rest of the list.

If there is no clear winner, subject lines with a low open rate will be discarded and the remaining subject lines will battle it out for a second hour, on up to 5,000 more records.

At the end of the second hour, the most opened subject line from the second test is chosen as the winner and sent to the rest of the list.

If you are sending the same message to a large list, the Subject Line Selector is a great option for improved open rate.

However, if your list has less than 10,000 valid records, Subject Line Selector becomes less effective as there will be not be enough records or time to choose a winner. This will also skew the reporting.

A good rule of thumb is only use Subject Line Selector if your list is well over 20k.

Alternatively you can use the “clean list” function, to delete any previously bounced and unsubscribed records from your list, before you schedule; this way you will have an accurate record count to decide whether to test or select your subject lines.

When choosing subject lines, try to decide on what you are testing for- for example, the length, position of main call to action (start, middle or end), testing of specific key call to action words themselves, emoji etc.

It also helps to get other colleagues to contribute, otherwise you are likely to end up with the same subject line rearranged in different ways. You can then use the results of your test to drive future subject line decisions.

To find out more about how to create inspiring subject lines, have a look at our blog section.