An important part of John Simpson's Combined Patch is the validrcptto.cdb patch which allows your server to check the RCPT TO argument and reject messages which were being sent to non-existent addresses. This is a great way to decrease the amount of spam your server has to process as dictionary attacks are a common spammer technique.
The validrcptto patch consults a CDB file, /var/qmail/control/validrcptto.cdb which should contain every valid email address and alias on your server. Rather than generate this list manually or try to create our own script to do it, we'll utilize John Simpson's mkvalidrcptto script.
