This information is in the Avast Help file, a good browse would be helpful. Manual setting of mail protection.
Step two: modifying the account properties in your mail program
Launch your mail program.
Let the program display the account settings.
If you want to check outgoing messages, change the address of SMTP server to the address of the local computer, i.e. 127.0.0.1.
If you want to check incoming messages, change the address of POP (IMAP) server to the address of the local computer, i.e. 127.0.0.1.
Change user (login) name this way: append the character # (double hash) and the address of your POP (IMAP) server (the same as you specified in the avast4.ini file in Step one). Login name should then look like this:
Ann.Jones#pop3.tiscali.com
If your e-mail program supports SMTP authentication and also makes it possible to set a different login name for SMTP than for POP
If the SMTP authentication is enabled, append the character # and the address of your SMTP server to the login name (e.g. annie2#smtp.tiscali.com).
If the SMTP authentication is disabled, enable it and use the character # together with the address of your SMTP server as the login name (e.g. #smtp.tiscali.com).
Save your changes.
The manual setting of the Mail scanner is now complete.