With 98\Me:
1. Configure your email accounts to work without the antivirus and test them.
2. If everything is fine, close all your email clients (programs).
3. Start Menu > All programs > avast antivirus > Mail Protection Wizard
4. Follow the non Outlook/Exchange option (i.e., the second one).
You can choose the supported email programs and select all the accounts
(even the ones created in the future).
5. Configure your email accounts to use avast! as antivirus.
With XP:
With Windows 2k\XP\Vista, avast has a new mail detection that will work automatically. Please, set up your email account just as avast does not
exist. It will detect the pop3/smpt/imap ports and scan your messages. Can you make a try and see if it's ok? Thanks.
New email detection is automatic and do not require user interaction. Anyway, spam killer applications need manually change email account settings
Hope this helps.
More information here:
http://forum.avast.com/index.php?board=9;action=display;threadid=4818;start=msg34754#msg34754