There must've been requests to make it easier to allow non-compliance in
Exim, specifically, allowing non-compliant characters in host/domain names.
As more and more small and medium size companies come online, Microsoft has
made it easier for them to manage their own mail without the benefit of a
normal sysadmin. As usual, though, when Microsoft breaks the rules, everyone
else is expected to alter their own behavior to comply with Microsoft's
non-compliance.
However... In this particular instance, (the implementation of MTA software)
Microsoft is still in the minority. I'm begging you guys, please don't start
allowing underscores or other illegal host/domain name characters just
because you have a reject log full of Microsoft hits. There must be a way to
make this more public; to force those who "administer" Microsoft software to
come into compliance.
From RFC2821:
----snip
To promote interoperability and consistent with long-standing
guidance about conservative use of the DNS in naming and applications
(e.g., see section 2.3.1 of the base DNS document, RFC1035 [22]),
characters outside the set of alphas, digits, and hyphen MUST NOT appear
in domain name labels for SMTP clients or servers. In particular, the
underscore character is not permitted. SMTP servers that receive a command
in which invalid character codes have been employed, and for which there
are no other reasons for rejection, MUST reject that command with a 501
response.
----snip
SMTP servers that receive a command in which invalid character codes have
been employed.... MUST reject that command
--
dana_booth <maullin@???>
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