When setting up Open fire, It asks for a domain and enters the current one for server its running on. The help suggests using the IP or hostname of the machine its running on. Is there any issue with creating your own name? I have tried in a test environment and it seems to work fine. I was thinking of mycompany.chat. This way users jabber account is email@example.com.
you may want to use the same domain name as you are using for email. This should make it more easy for users to get the XMPP address (bare JID) of other users in your company.