Jacob Palme writes:
- Members only: Only members are allowed to submit to the list
This causes huge problems with sublists, newsgroups, multiple accounts,
crossposted discussions, and other situations where a reader isn't
necessarily a subscriber.
(1) Add a "Received:" header to all messages passing the list. If a
mailing list recognizes its own "Received:" header in an incoming
message, such a message is dropped.
In practice, people use fields that are easier to parse than Received,
notably X-Loop and Delivered-To.
No non-delivery notification
should be sent in this case (since it might cause another loop).
Hiding loops is a horrible idea. Bouncing will never cause a loop if
it's done correctly; see http://pobox.com/~djb/proto/mailloops.txt for
details.
(2) Store a data base of the Message-ID-s of messages which have
passed the list, and reject incoming messages whose Message-ID
is on this list.
As noted in http://pobox.com/~djb/proto/immhf/thread.html, such uses of
Message-ID are neither secure nor reliable.
Apart from what is specifed in sections 8. Loop Control and 9. List
Headers, a mailing list expander should not in any way modify the
heading of a message.
This is astoundingly shortsighted.
---Dan