Did you run Mail Protection Wizard after installing Thunderbird?
You can certify showing the Headers of the message and looking for lines like these ones:
Technical… I believe that you have to fix the mail settings manually and Avast does not take care of them for Thunderbird. I read that someplace in one of the topics here in this forum after trying to get it to work with TB myself. After taking care of the settings manually, it works fine.
Even worse now. I just used the email test from Jason’s Toolbox and nothing caught the .vbs (harmless test file version) that was attached to the email.
avast! works with multiple smtp/pop servers and can protect as many pop3/smtp server accounts as you want:
Configure your email accounts to work without the antivirus and test them.
If everything is fine, close all your email clients (programs).
Start Menu > All programs > avast antivirus > Mail Protection Wizard
Follow the non Outlook/Exchange option (i.e., the second one).
You can choose the supported email programs and select all the accounts
(even the ones created in the future).
Configure your email accounts to use avast! as antivirus.
Note: the pop/smtp default servers are just the ‘default’ ones. They would be used to send files to Alwil Software (for virus analysis, for instance) and in special email accounts configurated to use ‘default’ servers.