I going to state the blindingly obvious but have you unchecked the inbound scan in the Internet Mail, Customise, POP3 ?

I’m at a loss as to why is scans outbound and not inbound if it can scan one it should be able to scan the other on less there is something about the email you receive.

Personally I would not use the ‘Insert note into clean message’ (if that is what you mean by the mail scan tag) with Incredimail, there have been lots of posts in the forums about Incredimail and the clean note problem for some if just doesn’t work and can cause malformed text layout in incredimail because avast inserts a clean note in the text and html parts of incredimail. For some reason that is something that can confuse incredimail’s layout. Though this should have no impact in the not scanning inbound email.

Is this a proper POP3 email account or a webmail account that you import into incredimail ?

Has avast ever scanned inbound email ?

What email port do you use in the incredimail email account settings for POP3 server ?
I have use my OE email account settings as an example, there should be a corresponding one in incredimail.