I have various Internet services like email, web and messages running on a Mini server running OS X on a subdomain.

Often, I want services like Messages to appear to use our main dot-com address, yet actually run on our internal dot-net domain.

So, how do I configure Messages server to appear to virtually function on our dot-com, yet still reside on a sub-domain?

For this discussion, let’s call that subdomain server.example.net. My business’ main domain is example.com and is hosted on another machine.

In this setup, users of our Messages service (which is really just an Apple-branded version of Jabber) must log in with account@server.example.net. That means for outsiders to connect with them, they have to share that address. But, what I really want is for my users to be available at account@example.com.

Configuring this was stunningly easy from the command line:

sudo serveradmin stop jabber
sudo serveradmin settings jabber:hostsCommaDelimitedString = "server.example.net,example.com"
sudo serveradmin start jabber

Simply put both domain names in the second line.

Next, we need to set up our DNS to forward Jabber (XMPP) requests from our main domain (example.com) to our actual server (server.example.net). This is accomplished with three separate SOA records:

_xmpp-client._tcp.example.com. 18000 IN SRV 0 5 5222 server.example.net.
_xmpp-client._tcp.example.com. 18000 IN SRV 0 5 5223 server.example.net.
_xmpp-server._tcp.example.com. 18000 IN SRV 0 5 5269 server.example.net.