Double POP3 scanning could due to avast4.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, for instance, change the line
PopRedirectPort=111
On the other hand, when you would setup all your mail clients as if avast! is not installed, you wouldn’t get a double scan. Your connections would be scanned just when they leave you PC - that is the communication between the email program and the POP3 server on the internet.
But, in fact, I’ll find if I can bring you more information about the one which destroys part of the email… Just I can’t find right now where is it 