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From: Jacob_Palme_QZ%QZCOM.MAILNET@MIT-MULTICS.ARPA
Newsgroups: net.mail.headers
Subject: Re: Checksum as a replacement for missing Message-ID.
Message-ID: <9144@brl-tgr.ARPA>
Date: Tue, 12-Mar-85 05:28:17 EST
Article-I.D.: brl-tgr.9144
Posted: Tue Mar 12 05:28:17 1985
Date-Received: Fri, 15-Mar-85 01:24:54 EST
Sender: news@brl-tgr.ARPA
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A further reason why it is necessary to create a Message-ID for a
message which does not have any: Checksums are necessary in order
to preserve in-reply-to-relations between pairs of messages which
may be transmitted between hosts via different routs.

Example: Host A sends out a message M1 to hosts B and C. at host
B, a reply M2 is written and sent to host B. In order for host B
to be able to recognize that M2 is a reply to M1, A and B must
independently generate the same Message-ID on M1.

Question: Why did I not include the value of the in-reply-to field
in the creation of the checksum. Answer: Because some systems may
allow the addition of an in-reply-to field after the creation of
a message. (At least we do. We sometimes get messages which clearly
are replies to other messages, but which do not have in-reply-to
fields. I sometimes then add an in-reply-to reference to the
incoming message, since the sorting of the message data base through
in-reply-to-relations makes it easier to use.)