Thunderbird doesn't have a concept of message numbers. I don't know any way to map the number Bitdefender finds to an actual message. I'd just let the message sit in the spam folder until it gets deleted automatically. Even with a potentially malicious attachment, it can't do any harm as long as you don't open any of them. I let Thunderbird delete spam messages automatically after 14 days. That gives you a chance to check for false positives. In general, letting the anti-virus on-access scanner scan Thunderbird mail files is dangerous, as it can cause mail file corruption and hence loss of data. It is therefore recommended to create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. http://kb.mozillazine.org/Profile_folder_-_Thunderbird For the same reason: Don't let your anti-virus software scan incoming and outgoing messages. Don't let your anti-virus software scan attachments.