Question : Changing FQDN in Split Brain Domain

I have a network that is configured as a split brain.  E-mails go out as name.org but internal DNS is name.net.  The FQDN on our exchange server has the .net. suffix (this is seen in the e-mail header info).  We have occasional 554 errors when organizations do reverse lookup as our ptr record (controlled by our isp)  shows mail.name.org. I can have the isp change our ptr record to match the FQDN on the mail server and I would guess this would fix the problem.  I was wondering:
 1.  What would happen if I changed the FQDN on the mail server to .org rather than .net?  This way, all e-      mail header info would reflect the .org suffix (originally what I wanted anyway).
 2. What changes would I need to make on my internal DNS servers (all MS server 2003)?
 3. What major headaches would I encounter?
 I realize I would need to have ptr changed no matter, what but I like the idea of the outer world only seeing name.org.
Thanks
SM

Answer : Changing FQDN in Split Brain Domain

Your reverse lookup has nothing to do what's in your headers as FQDN, the  important is what is the IP address of the source in the header. If the ip resolves to the MX record of your domain then you are fine.
Meaning, someone received an email, where in the header 69.212.23.16 is the IP of the source mail server, the receiving server will perform a reverse lookup on the ip address, then whatever the result is, it will go look for the domain to see, if that IP address is really the MX record.
So you are fine, unless the source IP in the header shows a different IP than the one registered in your PTR. Another thing you can do, is to add an SPF record. More and more. exchange admins are enabling the SPF, which is a good additional way of avoiding spam.
Regards.