http://www.faqs.org/rfcs/rfc1036.html
http://www.faqs.org/rfcs/rfc2119.html
THE MISSING MESSAGES DO *NOT* VIOLATE USENET RFC.
Here are some excerpts from RFC-1036 (which obsoleted RFC-850):
2.1.4. Subject
[...] If the message is submitted in response to another message
(e.g., is a follow-up) the default subject should begin with the
four characters "Re: ", and the "References" line is required.
[...]
2.2.5 References
[...] User interfaces need not make use of this header, but all
automatically generated follow-ups should generate the
"References" line for the benefit of systems that do use it, and
manually generated follow-ups (e.g., typed in well after the
original message has been printed by the machine) should be
encouraged to include them as well.
Based on this, I would definitely say that "Re: " messages without
a References header are in violation of this RFC.
EXCEPT that the statements are "should" (see RFC2119 noted above)
and the header itself is optional. No news software should reject
any message missing the References header, even if best practices
would indicate that the References header is strongly recommended
when "Re: " is present. Both In-Reply-To and References are
*optional* in RFC2822 (the successor to RFC822). The real problem
with RFC1036 is that it (1) requires English (e.g., "Re: ")
backreferences, and (2) attempts to codify usage rules with
technical rules.
So, no, technically, messages missing "References:" are not in
violation of RFC1036.
(And no, there's *nothing* that I can do to force them there in
Outlook.)
-austin