[link|http://kb.mozillazine.org/index.phtml?title=Thunderbird_:_FAQs_:_Anti-virus_Software|Here].
Note that Thunderbird 1.0 is [link|http://www.mozilla.org/products/thunderbird/|out].
Cheers,
Scott.
(Who has spent a couple of days trying to get TB 0.9 to work properly with [link|http://texturizer.net/thunderbird/faq.html#q2.12|digital signatures] without success - I can't send signed mail. :-< )