you can control avast behavior with these .ini file settings:

AutoRedirect=1
IgnoreLocalhost=1
PopRedirectPort=110
SmtpRedirectPort=25
ImapRedirectPort=143

Specificaly if you wanted to disabled port 110 and scan POP3 on 1123, change the line

PopRedirectPort=1123.

On the other hand, when you would setup all your mail clients (including ‘Popfile’) “as if avast! is not installed”, that is:

Outlook Express → PopFile at localhost:123 → pop3.domain.net:110 → (avast! transparent scanner) → pop3.domain.net:110

you wouldn’t get a double scan. Your connections would be scanned just when they leave you PC - that is the communication between PopFile and the POP3 server on the internet.