Just a quick note to warn anyone using Mozilla Thunderbird that there may be a critical bug in the way the client handles mails with SpamAssassin headers.

Users (including myself) have reported receiving alerts from TB of new mail that does not appear in any mailbox within the client. Manually scanning INBOX files in a text editor does reveal the mails.

It is not clear if this problem only affects mail with X-Spam-Flag: YES headers.

Do not compact our mailboxes as this may cause the permanent removal of mails that are hidden.

For the moment the best bet is to downgrade to 1.5.0.7.

More details can be found here.