Let Avast handle what, exactly? Does Avast 2014 provide server authentication and/or encryption like SSL/TLS? There’s nothing in the documentation that says that it does, so I’m not clear.

The program does clearly say, however, that it can now scan your email, even in a mail client with SSL/TLS enabled. To me, this means we shouldn’t have to disable SSL/TLS in TB. But either Avast and TB no longer play nicely, or nobody has stumbled upon the correct configuration.