"Mark" == Mark Crispin <mrc(_at_)cac(_dot_)washington(_dot_)edu> writes:
Mark> Now we hear the claim that completely unnecessary restictions
Mark> in headers are necessary because of news software.
who says those restrictions are unnecessary?
Mail systems do not appear to make any actual use of the message-id
header other than for logging (and internally in some odd systems).
None of SMTP, POP3 or IMAP ever use message-ids as protocol
parameters. News, on the other hand, uses message-ids as protocol
parameters _all the time_, both for readers accessing messages and for
server-to-server transfer.
FWIW, draft-ietf-imapext-thread-12.txt is the obvious counterexample. But even
if what you say is true about the present email transport infrastructure, there
are plenty of email clients that support threading via message-id.
(and, FWIW, I checked about a hundred thousand message-ids taken from
mail messages here, and only one of those had whitespace in and that
was a Chinese spam which had four spaces in place of the domain-part,
almost certainly due to misconfigured or broken spamming software. So
this clearly isn't a feature that anyone actually _needs_, or probably
even wants.)
Which of course is illegal according to any of the relevant standards.
Mind you, I'm not saying that additional restrictions on message-ids in news
are inappropriate. At a minimum the restrictions of RFC 1036 have to be taken
into account. However, I do urge caution when attempting to cater to failure to
support the existing specifications in the installed base, however. This is a
game that has to be played very carefully.
Ned