It's a feature to allow you to filter messages better. It also works if you add an addition symbol. For example, my.email+cnn@gmail.com would be the same as mye

It's a feature to allow you to filter messages better. It also works if you add an addition symbol. For example, my.email+cnn@gmail.com would be the same as myemail@gmail.com. If you wanted to know who sold your email to spammers, you could ideally go back and look at who the mail was sent to.