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From: netinfo%ucbjade@ucb-vax.ARPA (Postmaster + BITINFO)
Newsgroups: net.mail.headers
Subject: Re: Mail looping
Message-ID: <1307@brl-smoke.ARPA>
Date: Wed, 26-Feb-86 03:08:10 EST
Article-I.D.: brl-smok.1307
Posted: Wed Feb 26 03:08:10 1986
Date-Received: Sun, 2-Mar-86 19:32:48 EST
Sender: news@brl-smoke.ARPA
Lines: 49

Handling of mailing list error messages (Reply-to, Errors-to, etc) was
discussed at length in this mailing list group about a year or two ago.

The final conclusion was that "mailing list exploders" should generate
a new message (ie. with a new Message-ID). (The "Errors-to" header was
also disapproved if I remember rightly.)

In reply to:

	Date: Fri 21 Feb 86 11:47:35-PST
	From: Peter Karp <PKARP@sri-iu.arpa>
	Subject: Mail looping
	To: header-people@mc.lcs.mit.edu
	Cc: pkarp@sri-iu.arpa
	Message-Id: <VAX-MM(174)+TOPSLIB(114)+PONY(0)
		21-Feb-86 11:47:35.SRI-IU.ARPA>

	... Thus,
	"USER@Host-B" should receive two copies of the message: one direct from
	Host-A, and one with return path: @Host-C,@Host-B:Originator@Host-A.

The first message would have the original Message-ID and the new message
would have a new Message-ID generated by the exploder.

	Notice that the "same message" gets routed through Host-B
	several times, and that it would be incorrect for Host-B to
	think it has detected a loop simply based on the Message-ID
	created by the message originator (this has been pointed out
	before).  Also note that the "same message" gets sent to the
	same recipient several times (USER@Host-B), and it would also
	be incorrect for Host-B to suppress the duplicate simply
	because it sees two messages with the same Message-ID going to
	the same recipient.  Both of these conditions look like loops
	but are not.

To avoid this problem, I suggest that each SUB-LIST exploder also replace
the Message-ID with a new Message-ID. (ie. Mailing list exploders at any
level should generate a new message.)

The mail exploder should also change the envelope and/or mail heading so
that error messages are returned to that exploder's administrator.
(ie. to the lowest level exploder).

There is a basic assumption about mailing lists that may be wrong.  Can
we assume that list mail goes from the root to all branches without going
through the same node twice?

Bill Wells
netinfo%ucbjade@Berkeley.EDU