if you have a "real" static public IP where you are able to define DNS A- and MX-records and also reverse delegation you can simply set up UCS by using this hostname.
Otherwise, like with dynamic IP-addresses, you might run into problems, especially when trying to send e-mails to other domains.
You will have to configure a "relay host" in this case.
In case you are using a provider to receive mail for your public domain you should use fetchmail to feed the mailboxes in UCS.
Documentation is available at Chapter 13. Mail services .