I edited your post to eliminate the scrolling needed to view it all & moved this to SecurityCenter..
This is the first time I've ever heard of that. It's more likely a problem between McAfee and Thunderbird which would be best answered by McAfee's Technical Support Online Chat. See Useful Links above.
It isn't the firewall anyway but the antivirus application that is scanning your emails.
You can turn off Email Scanning in settings as it really is an extra level of protection that many regard as unnecessary as any malicious attachments would hopefully be eliminated anyway if clicked upon or saved to your hard drive.
What version of Total Protection do you have, 2009 (square taskbar icon) or 2010 (shield)?
I have the 2010 version (Shield).
As I am about to get on a flight for Europe I suggest you contact Technical Support Chat via Useful Links above. As I said I think it's a Thunderbird issue.