Does the service provider (telco) allow more than one IP address (more than one rfc 1483 tunnel) for your connection? Does the router require separate (unique) vc's for this to work? If the provider will allow you to do this then getting a connection for your mail server is a matter of getting the right machine to talk to the right interface on the router. Just a couple of ideas.
Good luck!
Andy
Now he wants to use another one of his publicly registered static ip's for his mail server, which we are trying to plug into one of the unused jacks on the built it hub on the R7100. The problem is that we can not get the R7100 to respond to more then one public address.