Email safety is pretty basic, with or without an antivirus. If it contains a virus many times it will install before your antivirus can stop it. Some even have the ability to turn off your AV long enough to install themselves. Or they will lie dormant until you start or shut down your PC. Then nothing is running that can stop them from invading.
Safe Email Practices# Attachments
Attachments require special attention. They could contain viruses - even if it's coming from the computer of a friend. Therefore:
1. Don't open attachments if you don't know who they're from
2. Even if you do know who it's from, if the subject line sounds suspicious, contact your friend before opening. Viruses often "spoof" the from address (masquerade as someone else - usually getting the name from an infected computer's address book - the infected computer could be a friend's which is why all email - even from friends should be held suspect.) Viruses also often try to come up with a compelling subject line to get you to open them.