It is probably easiest to understand how this system works by tracking a message from the mailing list to the newsgroup and then a message posted to the local newsgroup (gated to the mailing list) and see how they are handled.
3.1 Mail from the mailing list
Mail from the mailing list is sent to all subscribed mail addresses. A special mail alias is subscribed to the mailing list in question and so all traffic to and from the list is sent by the list server to this address.
When mail from the mailing list arrives at the local machine, the mail alias pipes the incoming message to
mail2news.pl. The mail alias also specifies the destination (local) newsgroup.
mail2news.pl script processes the message, applying news headers and then uses
inews to post the message to the newsgroup.
3.2 Messages posted to the local newsgroup
The local newsgroup is set up as a moderated group, as this allows us to take advantage of the email capabilities of innd. Any messages posted to a moderated group are not immediately submitted to the group. Instead, messages are emailed to the moderator of the group.
By declaring the moderator of the local newsgroup to be mailing list address, all locally posted messages to the newsgroup are automatically mailed out to the mailing list by
innd and only appear once they have been received back through
mail2news.pl which adds the necessary ‘approved’ line to the messages and are thus acceptable to innd for posting to the newsgroup.