The Golden Rule of Subject Line Testing

Last updated: 
July 25, 2022

Plus Ten Things You Should Test Regularly

The Golden Rule is to Plan Ahead.

Every Subject Line should be tested.Ideally your testing method should be an ABCD (4 Subject Lines) or more test and never less than ABC (3 Subject Lines). This approach is necessary to ensure you get a good sense what you want to test so you can plan ahead. Remember: More variables = Better results

A plan that lays out the variables you want to test and when you test them will not only save you time when it comes to writing your Subject Line - you’ll already know your content and how you’re going to approach it - it will give you better results.

What Variables Should You Test?

1.      Test extreme lengths

A lot of sources advise that you should limit your Subject Lines to about 35 characters. It appears most marketers - whether they know it or not - seem be following that advice. Looking at the data we found 63% of subject lines that are sent are between 20 and 65 characters in length. But here’s the rub: Subject Lines of that length tend to underperform!  

The data shows that if your idea of short is between 25 characters and 65 characters your Subject Line length tests are bound to disappoint.

1.      TestCTA’s

Although one of the key aspects of successful copywriting is telling readers what they need to do, this is often overlooked in Subject Lines, where the focus is often trying to catch attention rather than drive action. We found for one client that telling subscribers what to do by including a direct call-to-action (CTA) helped to boost engagement. So rather than just saying ‘Summer Sale’ it became ‘Summer Sale – take a look at the latest offers in store and online’.

2.      Test questions

Using a question instantly makes your Subject Line look and feel very different in the inbox. It also helps you come up with completely new ways of promoting your email content. For example, you might go from ‘Save 50% today’ to ‘New favorite suit? Save 50% today’ – a jump that would have been hard to make without the framework of a question.

 3.      Test original words

We’ve previously noted that using original words in Subject Lines can boost click rate by as much as 34%, yet less than a third of Subject Lines feature original words. Try using a thesaurus or taking inspiration from the dictionary definition to change some of your most-used words.

Learn how to optimize your Subject Line testing to get better results.

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4.      Test personalization

While first name personalization is common, it can still have a positive effect if you don’t overuse it. Look at available data fields to see what other personalization you can include in the Subject Line- such as surnames, recent purchases or locations including a city name can perform well, for example.

5.      Test external event and influences

We find that being reactive and riding on the back of current events is a great way of boosting response, but the lift often doesn’t last long because other brands jump on the bandwagon. The email itself doesn’t have to be themed, if your Subject Line makes sense and doesn’t mislead. For example, it could be as simple as sending ‘Bored of the golf? Escape with the top 10 weekend breaks during the Masters.’

6.      Test emoji strategically

Emoji can be used in 3different ways: syntactic (as punctuation), lexical (to replace a word) and illustrative (as a decorative or design element). It’s a useful framework that can help you test them effectively and strategically.

7.      Test tone of voice

Within a brand voice there is still a lot of room for variation in tone – for example in the difference between a promotional email and a service email. Try mixing them up where appropriate –so rather than ‘Hurry - check out our latest events’ you might use ‘We wanted to let you know’. But remember it’s about subtly changing the tone, not misleading customers.

8.      Test pronoun use

One of the first things you learn about copywriting is to use ‘you’ more than ‘we’. But ‘we’ and ‘our’ can be effective if your customer trusts your brand and sees you as an authority. Try positioning your subject line from both points of view and see which is more effective, for example instead of ‘Top picks for you’ you might try ‘Top picks from our team’.

 10. Test Punctuation & Separators

Punctuation and separators do make a difference and have a real impact on open and click rates, but the best results come if they are rotated. For example using an ! for emphasis or | to separate the different propositions within your subject line will only give a lift for a short period of time after which open and click rates will fall back to or even below average. So, a once and done test strategy will end in failure.

Keep Testing and Optimizing

The only way to stop your open rate performance from dipping over time is to keep your Subject Lines fresh! Once and done testing is does not work. Our Subject Line tool, SubjectLinePro, lets you test and optimize hundreds or iterations of your subject line in minutes. So, once you know your approach, you can continue to edit and improve it before every single email you send goes out.

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