Aaron C. de Bruyn via mailop wrote:
On Tue, Oct 8, 2019 at 1:51 PM Bill Cole via mailop <mailop@mailop.org
<mailto:mailop@mailop.org>> wrote:
Not exactly garbage: if it exists, it needs a '@' and the legal
content
is slightly less permissive than the 'addr-spec' definition (i.e.
email
addresses.) Also, it must be unique, so using a real fully qualified
hostname (i.e. one that no one else will use) is useful. OR: use
none,
and have your gateway generate one.
https://tools.ietf.org/html/rfc5322#section-3.6.
Yeah--I should have been clearer when I said 'garbage'.
I was pretty sure vaguely-readable line-noise separated by an @
qualifies. :)
As far as I am aware the 'domain side' of the @ in a message ID has no
requirement to be a valid domain. The message id should be unique - but
remember that is not just across your email system it is also across any
destination email systems (any email system where the email might reach
either as destination or transit) so using your own domain is a good
thing. Using <anything>.local is more likely to collide with other mail
servers not using their own domain names. All that said, message
servers that generate .local message ids are usually configured to see
.local internally and will often communicate internally with '.local' so
it could be the same messages were reporting 'helo' fields of
'hostname.local' which is often a sign of something internal
misconfigured or malicious... and many systems will use heuristics on
received lines/components for weighting towards spam.
Regards,
Michelle
--
Michelle Sullivan
http://www.mhix.org/
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