This is an infographic created by Salesforce.

There’s that old saying that you get one chance to make a great first impression. Here’s another thought: You get one chance to write a great email subject line and test it before your communication to current and potential customers ends up in the trash bin of email programs.

Many people assume that you write an email, you send it, and you’re done. But the most sophisticated email programs do something extra: They do what’s called A/B testing, also called split testing. A/B testing says that you’re going to develop two sets of email subject lines and test them on pre-determined groups that share some characteristics — perhaps they’re divided by age, for example, or where they live or income level.

The reason that A/B testing matters is that it helps you learn more about email and more about your customers. You learn what kind of messaging they respond to — and what kind they don’t respond to, either. Ready to learn more? This graphic can explain it.