3 Data Driven Email Subject Line Laws + 1 Bonus

After A/B testing email subject lines sent to large lists, I’ve noticed some small nuances in the way subject lines are written that seem to influence open rates.

1. Using special characters in the subject line tended to increase open rates by about 1%: Consider using + 1 Bonus rather than Plus One Bonus to increase open rates.

2. Using a combination of letters and small numbers such as 1, 2 or 3 in subject lines tended to increase open rates by about .5% to 3%. Subject lines such as “3 rules to increase open rates” performed better in testing than similar subject lines such as “Three rules to increase open rates.”

3. Shorter subject lines performed better than longer subject lines. While including adjectives is helpful, trying to squeeze in too many characters did reduce open rates in testing. So try to follow the best practice and keep your subject line to 50 characters or less.

Bonus Observation:

If sending out an email with multiple articles, products, or anchor texts linking to multiple landing pages, you can drastically increase the click through rate on 1, 2 or even 3 links by mentioning them in the subject line.