Dimidiate

When an unsolicited email makes an appearance in your inbox, never just delete it. Always mark it as spam. This is how the automatic spam filters learn to identify spam and filter it out.

Here's how to mark an email as spam in Gmail, Outlook, and Mail for Mac:

In Gmail, check the box next to a spam email, then click the "Report Spam" button.
In Outlook, right-click on the spam email in your inbox and select "Mark as junk.
In Mail for Mac, right-click on the spam email and click "Move to Junk."
Never publish your email address
Don't open suspicious emails
Don't give your email address to companies you don't know or trust
By doing all the above you can prevent spam emails to an extent though not entirely.