I entered 995 as the SMTP port (which gmail uses) I received a message about it being encrypted, I think that's when the 1st lock up happened, perhaps that's what caused the lock up.
That may well give a problem, but I don't know for sure.
If you had that same port number in your email client then it would fail as SSL has to be disabled to allow avast to rout it through its proxy so it can be scanned it then handles the secure connection.
So are you doing that in your email client ?
There should also be an associated entry for gmail in the avastUI, Mail Shield Expert Settings, SSL Accounts and that should reflect the correct port to connect to.
The problem being, I'm an avast user like yourself and I simply don't know (but suspect) if the email virus alert would be routed through the mail shield proxy.