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From: Jacob_Palme_QZ%QZCOM.MAILNET@MIT-MULTICS.ARPA
Newsgroups: net.mail.headers
Subject: Subject: Loop control mechanisms in mailing lists
Message-ID: <977@brl-smoke.ARPA>
Date: Mon, 17-Feb-86 00:08:16 EST
Article-I.D.: brl-smok.977
Posted: Mon Feb 17 00:08:16 1986
Date-Received: Wed, 19-Feb-86 01:04:09 EST
Sender: news@brl-smoke.ARPA
Lines: 37

Do mailing lists in Arpanet, Csnet, UUCP etc. usually contain
loop control, and if so which kind of loop control.

The most common methods for loop control are:

(1) Do not send a message to a member of the mailing list, if
that member is already in the TO, CC or BCC fields of the incoming
message, or possibly also some other field like SENDER, FROM?

(2) Save at least the Message-ID-s of the message passing the
list, and do not allow a message with the same ID to pass the
list twice.

(3) Organize the lists and sublists so that no loop occurs in
the structure.

(4) Expand all lists and sublists at one time at the original
sending of the message.

QZCOM at present uses method (1) and (2). I know that UUCP/USENET
uses method (2).

A problem with method (1) is that the name of the same recipient
can be given in many alias forms, and this will make it difficult
to understand that the name in the list and the name in the message
is the same.

A problem with method (2) is that all messages do not have any
Message-ID-s. Because of this, QZCOM always adds Message-ID-s
to messages sent to us and forwarded again from us to the nets.
At present we construct these Message-ID-s as <...@QZCOM>, but
a neater way would be to construct them from a checksum of the
from, date and contents, and then present them as <...@CHECKSUM>
as I have proposed in a message about a year ago.

I would be very interested to know which methods of loop controls
other mailing lists apply, and their experience with them.