Ler,
Firstly, when you set up Avast, did you use the Mail Protection Wizard, or did you configure manually?
Secondly, are you using the Pro or Home version of Avast?
Thirdly, what is your ISP? and mail client?
The simplest thing to do is one or both of these:
1. Rerun the Mail Protection Wizard.
2. If you are using Win XP, then go into Control Panel/Add_Remove and highlight Avast....then Remove.
At this point you will be given the option to REPAIR Avast. Click it .
It is hard to tell at this point what the cause of the problem is until I know more about your setup.
Thank you.
techie