5. Numbers in your subject line

A number in your subject line creates an expectation and gives you exactly what people are going to get. Comparative tests even show that subject lines with numbers dozens of percent perform better than without numbers.

To name a few:

8 email subject rules that make your newsletter more readable

40 tips to make your website more visible

3 steps to create more sales

Note: higher or lower numbers play a role.

You do not want to go over 40 steps to more sales

2 email subject rules would be a scary number.