email problem

I got so many emails with subject like this "Warning: message 1Gaqw2-0002w6-TL delayed 72 hours", the body messege looks like this:
This message was created automatically by mail delivery software.
A message that you sent has not yet been delivered to one or more of its
recipients after more than 72 hours on the queue on server1.maxsource.net.

The message identifier is: 1Gaqw2-0002w6-TL
The subject of the message is: RE: SH
The date of the message is: Fri, 20 Oct 2006 17:44:35 +0800

The address to which the message has not yet been delivered is:

parousia@timnen.cotse.net
Delay reason: SMTP error from remote mail server after MAIL
FROM:<daily@max-source.com>:
host mailhost.cotse.com [216.112.42.58]: 451 4.7.1 No RDNS:
Sender IP address is not resolving:
http://mail.cotse.net/cgi-bin/automatic-whitelist.cgi?h=nrdns

No action is required on your part. Delivery attempts will continue for
some time, and this warning may be repeated at intervals if the message
remains undelivered. Eventually the mail delivery software will give up,
and when that happens, the message will be returned to you.


What is the problem?

 

1. Would it be a problem at max-source.com server?
2. How could I check the ip address of timnen.cotse.net is not blocked on your server? BTW, we have sent emails to parousia@timnen.cotse.net before and there is no problem.
3. I checked exim_mainlog on our server, and i saw many texts like below which are related to this issue.
2006-10-24 06:19:11 1Gaqw2-0002w6-TL == parousia@timnen.cotse.net R=lookuphost T=remote_smtp defer (0): SMTP error from remote mail server after MAIL FROM:<jackieh@max-source.com>: host mailhost.cotse.com [216.112.42.58]: 451 4.7.1 No RDNS: Sender IP address is not resolving: http://mail.cotse.net/cgi-bin/automatic-whitelist.cgi?h=nrdns
2006-10-24 06:19:11 1Gaqw2-0002w6-TL ** parousia@timnen.cotse.net <parousia@timnen.cotse.net>: retry timeout exceeded

And in the end, i saw this text: 2006-10-24 06:19:11 1Gaqw2-0002w6-TL Completed
Dose this line mean that this message has been sent out successfully?