I recently switched to notmuch, and I'm mostly happy with it. I do
however have one issue: my mail server runs SpamAssassin, which tags the
subject header of mail considered spam with »[SPAM]«.

I've been trying to get notmuch to apply the tag »spam« to these mails,
but it seems I can neither make it search for upper-case letters nor
»[«/»]«. My current solution is to tag everything with »spam« somewhere
in the subject header as spam, which leads to lots of false positives.

Also, and much less importantly, is there any way to have notmuch
harvest email addresses for BBDB?

Any advice on how to fix this would be appreciated.