I too get the annoying ssl pop ups. I use Postbox express with imap gmail.
I tried to resolve the problem using the tips I found here, moved the server
to keychain system, disabled ssl on Postbox, added server on avast advanced
setup, and several combinations of all the tips, but nothing,...
Postbox tries to access gmail but nothing... endless activity donut...
I finally turned everything back to the original setup and disabled avast mail shield.
I'm disappointed with the way Avast tries to tackle email protection, the solution
should be a simple drop in, you can't expect the users to start fiddling around with
system configuration options just to get Avast to work...
This is a -1 for you Avast, I'm keeping you around a while to see how everything
else works and hopefully you'll resolve the email problem with the next update !!