Is there a learnable filter in Thunderbird for non-spam messages (as in Opera Mail)?
One feature I like very much about Opera Mail is that you can have learnable filters for any purpose. So not only can you filter spam messages but also messages that your friends sent you or info mails from web platforms without having to enter each and every mail address you want to filter. It actually works quite satisfying and you can combine it with string filtering, too. It does a few mistakes in the beginning but then improves quickly after you have removed some of the false positives.