Qmail does it unconditionally (and uses DNS ANY queries in the process).
Qmail's been abandonware since 1998. Everyone who still uses it has
patched it extensively, and we got rid of the ANY query ages ago. I don't
think it ever rewrote CNAMEs in message headers. I don't see code to do
it in either qmail-inject or its slightly newer replacement new-inject.
If I were doing an update to 5321 my non-negotiable preconditions would be
that changes are only allowed to describe existing practice in non-trivial
amounts of mail, that it obsoletes every previous definitions of SMTP, and
that it's published as a full standard. Once we spend a year agreeing to
that, the rest is easy.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail.
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