You should give some thought as to what your official local host name should be prior to configuring PMDF. This is not just a matter of picking a name for your system; if you wish to communicate with systems on the Internet your system will have to be registered as a member of some network domain. In order to be eligible for registration you must have a connection to a system on the Internet which is able to perform name server functions for you.
If you are using PMDF in an isolated (non-Internet) application you may pick any system name that you want. However, you should remember that networks have a way of growing and at some point in the future you may regret a careless decision about naming conventions you made earlier. Try to pick a sane, sensible name which is appropriate to your users, system, and site.
If you've already chosen a TCP/IP hostname, you might use that as your official local host name. Alternately, you could use a more generic e-mail hub name for your official local host name. Should you choose to do that, the PMDF configuration generator will also need to know your TCP/IP hostname. It will prompt for that, with a default answer, when asking about your TCP/IP network.