Explanation

As the comment on the condition flag indicates, this router (or director) is used only messages that meet the following criteria. You are free to adjust this condition to suit your site.

• wasn't received from spamassassin (determined by $received_protocol)
• wasn't received via a pipe from a local user (the assumption is that your local users won't be generating spam, so scanning their messages is wasteful of resources)
• isn't already flagged (this is safe because the only flag that is checked is a positive flag; spammers can tag their spam for you, but they can't tag it as being clean).