Welcome to forums…
Are you using Windows XP or 98\Me?
avast! works with multiple smtp/pop servers and can protect as many pop3/smtp server accounts as you want:
With 98\Me:
- Configure your email accounts to work without the antivirus and test them.
- If everything is fine, close all your email clients (programs).
- Start Menu > All programs > avast antivirus > Mail Protection Wizard
- 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).
- Configure your email accounts to use avast! as antivirus.
With XP:
With Windows 2k\XP, avast 4.5 has a new mail detection that will work automatically. Please, set up your email account just as avast does not exists. 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 
Edit: Glad that you solve it… It took me a long time to write this and I have to leave… So, you were faster :-[ :-\