This document outlines some of the best practices that you can follow to avoid email abuse.

Password Strength Configuration

If you increase the minimum password strength for your users' mail accounts, you can decrease the chance that a hacker will correctly guess their passwords.

Never respond to spam

If you recognize something as spam before you open it, don't open it. If you open it and then realize its spam, close it. Do not click a link or a button, or download a file, from a message that you even remotely suspect is spam.
If you opened spam because it appeared to be coming from a friend or co-worker, contact them immediately and let them know that their account has been compromised.

Hide your email address

The more people who have your email address, the more spam you going to get. So keep your address close to your chest.

Change your email address

This is a very drastic option, but if you responded to spam in the past or haven't hidden your address, and are therefore overloaded with spam, it may be your best option.
Of course, you all have to inform your legitimate contacts about the change, and you all probably have to keep both addresses for a few months. But once you can get rid of the old address, your spam count should plummet.