Re: [Emacs-diffs] /srv/bzr/emacs/trunk r104691: Don't reuse previous Message-id when resending.

[Stephen J. Turnbull]

Richard Stallman writes:

 > Using a new Message-ID can't do any harm.

Maybe not to you, but in case of partial failure it will create a new
subthread, confusing participants in the original thread.

 > It isn't wrong.

Sorry, Richard, that is not yours to decide.  This change is OK for
your personal version of Emacs, but in general it is the sender's
decision, not the implementer's.  From RFC 5322:

      In all cases, it is the meaning that the sender of the message
      wishes to convey (i.e., whether this is the same message or a
      different message) that determines whether or not the
      "Message-ID:" field changes, not any particular syntactic
      difference that appears (or does not appear) in the message.

For *most* users *most* of the time, a "retried" message should have
the same Message-ID (eg, if only some destinations failed).
Defaulting to same Message-ID is very safe as long as the content
doesn't change.  On the one hand, users are very unlikely to perceive
them as "different."  On the other, getting multiple copies of a
message with the same Message-ID is a common occurrance, and any
program dealing with Message-IDs should be able to deal with it.  But
defaulting to different Message-IDs does cause harm in the case of
partial retries.