I received a Messages Status - Undeliverable email from our GroupWise 2014 system. I've included a sample of the error details below; with personal info changed. The message said Response: 550 Denied! reverse DNS lookup failed. Essentially, one of our users sent an email to a particular person outside our organization and their email server bounced the email back to us due to reverse DNS lookup failure. I checked our reverse DNS record at our ISP and it is, in fact, setup properly. Additionally, we do not normally have any issues with sending emails outside our organization. I did some reading on the Internet about this issue and I read that some people report that if the domain in the email's Message-Id is different than the sender's email address, this can sometimes result in a reverse DNS lookup failure. Our Message-Id does show our old domain name.
I looked in the settings for our GWIA and I do see our old domain name in Hostname/DNS "A record" name:. I am thinking of changing this to our new domain name, because I suspect this will change the domain in the Message-Id in our outgoing emails to our new domain. Which, in theory should eliminate this issue that we are having sending emails to this one person. As a result, my questions are as follows:

1.) Will changing the Hostname/DNS "A record" name: in my GWIA to our new domain name solve the problem that I am having?
2.) Is there any chance that making this change to my GWIA will break our GroupWise system's ability to send/receive emails to the Internet, or otherwise break our GroupWise system?

Transcript of session follows:
Command: clarstate.com
Response: 550 Denied! reverse DNS lookup failed

Received: from unitma-MTA by mail.unit.tec.pa.us
with Novell_GroupWise; Wed, 29 Oct 2014 09:45:47 -0400
Message-Id: <5450B73E0200003F00024404@mail.unit.tec.pa.us>
X-Mailer: Novell GroupWise Internet Agent 14.0.0
Date: Wed, 29 Oct 2014 09:45:34 -0400
From: "George Williams" <gwilliams@unitcoop.org>
To: <info@clarstate.com>