Let's say your mail server gets a RCPT TO
for a domain it doesn't recognize, e.g. RCPT TO:<bob@f?om>.
Before it rejects it, it does a DNS lookup, and let's say it
finds this CNAME:
f?om. IN CNAME foo.com.
(2) The example, as written, is simply invalid. SMTP does not
allow single-labels domains.
Your MUA seems to have smashed my UTF-8. That was fXX.com where the X's
were o's with accents, really xn--f-vgaa.com so it was
xn--f-vgaa.com CNAME foo.com
e.g., if
f?om. IN CNAME foo.com.
exists, then there can be no b?ar.f?om because "f?om" usually
cannot have both a CNAME and a delegation record.
Let's say we wave our hands here and say it was a DNAME at a higher level,
like the one in Taiwan, or maybe someone does BNAME or CLONE.
Also, with respect to the sendmail thing, that was back before there was
much of a line between submission and relay, and I believe that was
intended as a submission fixup to implement the old rule that CNAMEs have
to be resolved before you send the mail.
Am I missing something? Is there a serious proposal being worked on to
try and specify this nonsense? If not, why should we bother?
No, I just wanted to be sure I hadn't missed anything interesting.
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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