How do I report a whole mailbox full of spam to Razor? SpamAssassin only handles single mail messages.
Theo Van Dinter, one of the SpamAssassin developers, has written a script which does this, along with some other reporting features. It can be picked up at
http://www.kluge.net/~felicity/random/handlespam.txt
Another simple approach (reported by Seth Arnold) is to use formail, from the procmail package:
formail -s spamassassin -r < /tmp/spam