address not listed for hostname?

This message has been bouncing from my system all day:

May 28 23:54:07 localhost postfix/smtpd[1574]: warning: 65.54.161.27:
address not listed for hostname bay106-f18.bay106.hotmail.com
May 28 23:54:07 localhost postfix/smtpd[1574]: connect from
unknown[65.54.161.27]
May 28 23:54:08 localhost postfix/smtpd[1574]: NOQUEUE: reject: RCPT
from unknown[65.54.161.27]: 450 Client host rejected: cannot find your
hostname, [65.54.161.27]; from=<xxx@hotmail.com>
to=<xxx@wrightthisway.com> proto=ESMTP helo=<hotmail.com>
May 28 23:54:08 localhost postfix/smtpd[1574]: disconnect from
unknown[65.54.161.27]

This error is making no sense to me, I've tried several times today to
do a lookup on bay106-f18.bay106.hotmail.com, and it properly resolves
to 65.54.161.27. I've even sent myself a number of test messages from
hotmail (about 20), and consequently got deliveries from a number of
other hotmail systems, but never that particular one. I can't seen to
figure out what is causing this error to occur...