[Mailman-Users] Tangential Delivery Question

[David Hwang]

I know this is probably tangential to the purpose of the list, but

people here have been very friendly and helpful in my quest to get 
mailman up and running on my Trustix system.

I was following the mail delivery logs and came across some odd errors 
that I'm hoping someone can help me decipher and  ultimately find a fix.

Or if someone has a suggestion where a better place to ask might be, I'd 
appreciate that as well.

This is what I'm seeing:

Nov  8 01:10:04 m5 postfix/smtp[1035]: 9CD0117F3B: 
to=<jblumberg at comcast.net>, relay=gateway-s.comcast.net[63.240.76.26], d
elay=58387, status=deferred (host gateway-s.comcast.net[63.240.76.26] 
said: 450 [TEMPFAIL] comcast.net requires valid sende
r domain (in reply to RCPT TO command))
Nov  8 01:10:04 m5 postfix/smtp[1040]: 9608F17F45: 
to=<hotyakker at comcast.net>, relay=gateway-r.comcast.net[204.127.198.26],
delay=13841, status=deferred (host 
gateway-r.comcast.net[204.127.198.26] said: 450 [TEMPFAIL] comcast.net 
requires valid s
ender domain (in reply to RCPT TO command))
Nov  8 01:10:05 m5 postfix/smtp[1043]: 5B71317F43: 
to=<jhwang at comcast.net>, relay=gateway-r.comcast.net[204.127.198.26], de
lay=5035, status=deferred (host gateway-r.comcast.net[204.127.198.26] 
said: 450 [TEMPFAIL] comcast.net requires valid sende
r domain (in reply to RCPT TO command))
Nov  8 01:10:07 m5 postfix/smtp[1030]: 6F0C917F47: 
to=<jhwang at comcast.net>, relay=gateway-r.comcast.net[216.148.227.126], d
elay=4409, status=deferred (host gateway-r.comcast.net[216.148.227.126] 
said: 450 [TEMPFAIL] comcast.net requires valid sen
der domain (in reply to RCPT TO command))


What does "comcast.net requires valid sender domain (in reply to RCPT TO 
command))" mean?

I assume that I've got something wrong in my configuration (Postfix, 
Spamassassin, Amavisd, Mailman) or in my DNS, but where should I start 
debugging?

Thanks,
David Hwang