I use an IMAP gmail account with thunderbird, so I can only speak for that one.
Normally there should be no problems with the email (besides avast! not being able to scan it)
Have you added the ports to avast! internet mail scanner?
This would leave you with a connection timed out error for imap and the error in the pic below for smtp.
Maybe it is the 4.8.1348 beta build, but adding the relevant ports to generate the error messages with a comma didn't work...it still came through but wasn't scanned