ietf.org mail blocking?

["Eric Rescorla" <ekr at rtfm.com>]

When I submitted my position paper today for the IETF RFC , I was a little
surprised not to get the promised acknowledgement. A little digging
around revealed that my mail was getting rejected by the IETF
mail server, first with a timeout during initial hello:

May  9 10:20:21 romeo postfix/smtp[13301]: 20EBC5081A:
to=<p2pi-com at ietf.org>, relay=mail.ietf.org[64.170.98.32]:25,
delay=304, delays=0.69/0.01/303/0, dsn=4.4.2, status=deferred
(conversation with mail.ietf.org[64.170.98.32] timed out while
receiving the initial server greeting)

and ultimately with a reverse resolution failure:

May  9 10:53:37 romeo postfix/qmgr[865]: 20EBC5081A:
from=<ekr at networkresonance.com>, size=148644, nrcpt=1 (queue active)
May  9 10:54:49 romeo postfix/smtp[13621]: 20EBC5081A:
to=<p2pi-com at ietf.org>, relay=mail.ietf.org[64.170.98.32]:25,
delay=2372, delays=2299/0.02/72/0.02, dsn=4.7.1, status=deferred (host
mail.ietf.org[64.170.98.32] said: 450 4.7.1 Client host rejected:
cannot find your hostname, [74.95.2.173] (in reply to RCPT TO
command))


Note that my IP actually does resolve, though I admit not to the name
of my machine. You
can blame comcast for this one.

limbo-randy3:~> nslookup 74.95.2.173
Server:         66.33.216.127
Address:        66.33.216.127#53

Non-authoritative answer:
173.2.95.74.in-addr.arpa        name = 74-95-2-173-SFBA.hfc.comcastbusiness.net.

Note that (unsurprisingly), this doesn't apply just to p2pi. A test
message to tls at ietf.org
(to which I assure you I am subscribed) gets the same treatment.

May  9 11:37:45 romeo postfix/smtp[14705]: 0EBE750823:
to=<tls at ietf.org>, relay=mail.ietf.org[64.170.98.32]:25, delay=118,
delays=0.13/0.05/118/0.02, dsn=4.7.1, status=deferred (host
mail.ietf.org[64.170.98.32] said: 450 4.7.1 Client host rejected:
cannot find your hostname, [74.95.2.173] (in reply to RCPT TO
command))

Note that I used to be able to send mail to tls at ietf.org from this
machine just fine, so something
has change.

Not sure what's going on here, but this seems like a new and rather
undesirable configuration setting.

-Ekr