I posted a question about this on the Tech Support forum. Here is what I'mNoPrince posted in reply:
I think that what is happening with all the blank e-mails is that the system is trying to send you notices about your subscribed threads, but since the database crash yesterday, the notifications aren't working.
I did what I'mNoPrince suggested & it worked. I still have my subscriptions and can go into my List to check them, but now I don't have to receive any more empty e-mails

. Hopefully Alex or one of the other Webmasters can get this fixed soon.
agnes!