Yes, it may block.
VSE AP, Antivirus standard protection=>Prevent mass mailing worms from sending mail may block this
To verify this, I will suggest you to look into Access protection log file.
If Thunderbird.exe is blocked by VSE AP then we have to add th exe to AP exclussions under the rule category 'Antivirus standard protection=>Prevent mass mailing worms from sending mail'.
Again rememeber, if the file is of more than 16 characters (In this case) then exclussions with complete file name (thunderbird.exe) will not work.
Either you can use Wildcard exclussion or can use HF 'VSE870HF613356.Zip' attached in KB#:KB70202.
What did you do?
Did you add Wildcard in the exclussion or applied HF?
3/25/2011 2:33:01 p.m. Blocked by port blocking rule C: \ Program Files \ Mozilla Thunderbird \ thunderbird.exe virus Standard Protection: Prevent mass mailing worms from sending emails 184.108.40.206: 25
I think, you didn't exclude correctly. Please share the screenshot for the exclussion for our review.