1. Only connections to SMTP, POP3 and IMAP ports are diverted to Mail Scanner (25,110, 143 - if not specified otherwise in the avast4.ini).
2. Once the connection is redirected to Mail Scanner the network filter no longer iterferes with it by no means.
3. It is possible to disable this feature in avast4.ini file (section [MailScanner] option AutoRedirect=0, but you will definitely NOT gain any speed improvement.