Here is the scenario, I have a company that I am doing work for and they have a AD Domain name of xyz.com. They do not want to host their own email and are using an outside provider. At one time their provider said to use mail.xyz.com for pop and smtp. So I looked up the external IP's of that server (mail.xyz.com) and created a local A record for mail.xyz.com that point to the external IP address. Everything was happy at this point.
Now the email provider is making all kinds of changes and wants them to use xyz.com in for the pop and smtp settings. This will cause a problem since xyz.com is their AD domain name. Now I can keep mail.xyz.com in their pop and smtp settings, externally query xyz.com from the provider and make a change to the local A record and things should be fine.
The problem is if the IP address for xyz.com changes and if I don't query the external ip, then mail will be down. I'm trying to avoid renaming the domain :) and looking for other suggestions.