Well each to her own taste .....
However, avast cannot tell the difference between an email program and a hole in the road. avast knows nothing about email programs.
avast instead intercepts what email programs do.
avast assumes that any program that makes a call to a server at ports 25, 110, 143 is doing so for email purposes (unless the program name is in a list of exceptions avast has) and avast proceeds to takeover and manage those connections expecting an email dialog to occur.
Since Incredimail has to do what every other email client does - avast will intercept what it does too.
Same old caveats apply - this is standard POP/SMTP mail. Anything in Incredimail received using those third party apps like FreePops, YPops etc still will be under avast's radar by default.