Ad blockers can only 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, otherwise 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. We recommend trying the suggestions in this article from Popular Science: How to stop spam emails from destroying your inbox.