I thought I had posted this on LSTSRV-L in the past, but here's the 
CONTENT_FILTER I use, for reference:

From::
Action: DISCARD No From: header, probably spam
Subject::
Action: REJECT Please resubmit your message with a non-blank subject.
Subject: out of office
Action: DISCARD Probable OOO message
Subject: out of the office
Action: DISCARD Probable OOO message
Text: I will be out of the office
Action: DISCARD Probable OOO message
Subject: Auto-Generated:
Action: DISCARD Probable OOO message
Subject: AutoReply:
Action: DISCARD Probable OOO message
Precedence: junk
Action: DISCARD Probably OOO or other non-germane message

Nathan