Ad blockers block ads that appear on web pages you visit or that your email provider inserts in your inbox. They can't block unwanted email sent by third parties, fondly known as spam. It's the digital equivalent of junk mail.
The unfortunate truth is that you will probably never be able to avoid spam altogether. However, you can reduce the amount you receive. If you use a Mac, please try the suggestions in this MacWorld article. If you use a Windows computer, please try the suggestions in this PC World article or this one from Popular Science.
You can also use the built-in spam options that are provided with your email service provider. The more you mark offending mail as spam, the less you will receive!