System i mail server not properly identifying itself

The System i is our mail server. We have a particular domain (msdsc.org) we cannot email to. We get (after a good hour or so) the following:

NOT ABLE TO DELIVER MAIL TO SOME/ALL RECIPIENTS.
REPLY CODES WITH FIRST DIGIT = '4' OR '5' ARE ERROR REPLIES.
ERRORS THAT DO NOT HAVE ERROR REPLY CODES MAY EXIST.

HOST I5 NOT ABLE TO DELIVER MAIL TO FOLLOWING RECIPIENT(S):
<xxxxx@xxxxxxxxx>
RETRIES EXHAUSTED WHILE ATTEMPTING TO CONNECT TO REMOTE HOST msdsc.

** TEXT OF MAIL FOLLOWS **
Received: from [192.168.0.35]([192.168.0.35])
by I5.DILGARDFOODS.COM (IBM i5/OS SMTP V05R04M00) with TCP;
Thu, 28 Feb 2008 14:07:56 -0500
Message-ID: <47C7068B.40304@xxxxxxxxxxxxxxxx>
Date: Thu, 28 Feb 2008 14:07:55 -0500
From: Jeff Crosby <xxxxx@xxxxxxxxxxxxxxxx>
User-Agent: Thunderbird 2.0.0.12 (Windows/20080213)
MIME-Version: 1.0
To: xxxxx@xxxxxxxxx
Subject: Test
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

The tech guy at msdsc.org says it's a reverse DNS issue. I got our Network Guy in (who does not understand System i) and he determined the System i was not properly identifying itself. He determined that from the following PC session:

220 Ready
helo i5.dilgardfoods.com
554 Connection refused: Connecting client IP doesn't match the host it claimed to be
during HELO. Failed to find any correlation between the claimed host
(i5.dilgardfoods.com) and the connecting IP (63.xxx.xxx.xxx).

I ass-u-me this is because the System i is identifying itself as i5.dilgardfoods.com which is not valid outside our LAN. As a mail server, it is known in the world as mail.dilgardfoods.com. Is the answer that the System i smtp server must somehow identify itself as mail.dilgardfoods.com? If so, I could not find anywhere in CHGSMTPA or iNav where this could be done. In CFGTCP I have both i5.dilgardfoods.com and mail.dilgardfoods.com under 192.168.0.1.

Thanks for any help.