lammert - 12:07 am on Jan 20, 2010 (gmt 0)

procmail checks the contents of the email after processing. You could add an extra header line to the message, for example X-Real-Junk: Yes. The following procmail lines will send that message then to the write-only /dev/null mailbox.

:0:
* ^X-Real-Junk: Yes
/dev/null