Filtering by source or destination channel provides greater flexibility and granularity for spam filtering. For example, you may wish to filter in these ways:
Only messages from a specific MTA relay to a backend message store
All incoming mail from a specific MTA.
All outgoing mail from a specific MTA.
Incoming and outgoing mail from a specific MTA.
Messaging Server allows you to specify filtering by source or destination channel. The mechanism for doing this are the channel keywords described in 12.12.5 Spam Filter Keywords. The following example demonstrates how to set up channel-level filtering.
Add a rewrite rule in the imta.cnf file for all inbound SMTP servers that send messages to a backend message store host. Example:
Add a channel corresponding to the rewrite rule with the destinationspamfilterXoptin keyword. Example:
tcp_msg_store1 smtp subdirs 20 backoff "pt5m" "pt10" "pt30" \ "pt1h" "pt2h" "pt4h" maxjobs 1 pool IMS_POOL \ fileinto $U+$S@$D destinationspamfilter1optin spam msg_store1.siroe.com