Like the OP, I'm having problems with the Mail Shield. I'm also running avast 2014.9.0.2021 (no update available) on Windows7/64bit, virus definitions up-to-date. I was on an earlier version of Thunderbird when the problem started early this morning. Found this thread, saw there was an update to Thunderbird, so I applied it.
Like the OP, I tried changing avast to remove the Mail Shield, reboot, reinstall the Mail Shield, and a finally reboot to activate it. Unlike the OP, my problem is confined to NetZero's SMTP server. I have four accounts from three providers in Thunderbird. Only attempting to send via NetZero's server results in the error. All my accounts are set to use SSL for inbound and outbound.
After removing the Mail Shield and rebooting, Thunderbird asked me to verify the exception for each account, going both ways (so, eight exceptions verified). After that I could receive and send mail. After I re-installed Mail Shield and rebooted to activate it, I was again asked to verify the eight exceptions. I still can't send via NetZero's SMTP server. I've attached a screenshot of one of the error instances (they always take the same form). If I disable scanning of outgoing mail, I can send via NetZero.
I'm not sure if this problem is related to avast, Thunderbird, NetZero or some combination thereof.
Any advice would be appreciated. For now, I'm not scanning outgoing email.
TIA.
I am using Avast 2014.9.0.2021 (no update available) on Windows7/64bit and also virus definitions are up to date, but since updating to Thunderbird 31.0 I cannot receive mails. Disabling the mail shield in the Avast settings > Active Protection >> Mail Shield = OFF the problem is solved.
First I only expected Thunderbird ha a problem after the update from 24.6 (I believe it was) and reinstalled the mail client but no effect. Of course I also rebooted my computer without any effect.
I have configured Avast to scan inbound mails and newsgroup messages - nothing comes in, no error message from Avast or Thunderbird but I was able to send a mail. Activating outgoing mail check has at least no effect on inbound mails