Email subject lines: To sell or not to sell, that is the question

Jeanette Lewing

07 January 2013

Unfortunately, there is no single solution or magic formula when it comes to email subject lines; what works for one campaign might not work for another. However, I’ve pulled together some guidance on how to better construct subject lines.

The key is to Tell NOT Sell. Subject lines get a better response when they are clear, factual and informative about email content, rather than misleading. Branding in a subject line can increase open rates, as it usually verifies a trusted source. However, it does use up valuable keyword space. Instead, you could consider clearly branding the sender line, top lines in the email, and content within the preview pane.

I’d also suggest using a dynamic subject line, which pulls relevant data for individuals or a segment of your audience - this may be by location or a particular preference.

Character length
There is some debate around the ideal length of a subject line, with research varying on whether longer or shorter subject lines are better. The fact is that some email clients allow more characters in a subject line than others, but most give at least 40/50 characters including spaces. So the key is ensuring that the main offer is at the beginning, ideally within the first 40 characters. Also bear in mind that subject lines can get truncated by email systems, although they may look fine in the preview window.

A good approach is keeping characters to a minimum, but this should not be damaging to the message. If it delivers the message better, make your subject line a bit longer.

Two key tips here. First, maintain a consistent “From Address” and “Subject Line Recognition” to help recipients see the email is from a trusted source. Second, avoid writing like a spammer. There are a number of attributes of spam emails, including subject lines which are ALL CAPS, highlighted words and excessive use of exclamation marks. There are also some spam-trigger words which are important to be aware of. If you can’t avoid using these words, I’d recommend only using them once in the email body.

To double check you can run the copy of your email through a content checker, such as Exact Target’s content detective.

Success measures
The best way to discover which subject lines are more successful is to continuously test them, analyse the responses and optimise accordingly. Split (A/B) testing can be an effective way to do this – take 20% of your subscribers, send half of them an email with one subject line, and the other half a different subject line. Monitor the results for perhaps 48 hours to a week, then determine which has been the most successful and send that email with the winning subject line to the remaining 80% of subscribers. This might also show how a subject line has appealed to your audience and therefore how to best set up your next campaign.

Remember that high open rates don’t always mean a subject line has been successful. The focus should be on the campaign’s end goal, which could be high conversion rates, event registrations, downloads.