Adds the previous host through which a mail message passed to the Path header of the message. It does this by looking through the raw Received headers, finding the first Received header that specifies a host from which the message was received, and prepending it to the Path header (or creating a new Path header if none already exists).
If no Received headers that contain a "from" clause are found (which may be the case for mail originating locally), nothing is done.
The reason for this module is to support news to mail and mail to news gateways for the same unmoderated newsgroup. If the mail to news address is subscribed to a mailing list and posts to the newsgroup are sent back to the mailing list, a loop will be created unless something is done to stop it. One method of stopping such loops is to alias the hostname of the mailing list machine out of the feed to the news to mail gateway in the news server and then use this module to put the hostname of the mailing list machine in the Path of all articles posted through the mail to news gateway.
This module takes no arguments or configuration directives and cannot fail.