Varjostin, There are two types of turn files, one contains the players directives to the host and the other update the player with the new turn from the host. Those files are form the hosting mechanism for dom (single player works the same). The first type of files (.2h) need to be sent to the host and the second type (.trn) need to be distributed to the players. The "carrying" layer is not really important, email is convenient but it could have been done using ftp, http or a costumized client (an example of a very customized client over TCP/IP is dominions
).
So it doesn't matter what email program you use as long as you are able to send and receive files.
It is possible that I've miss understood you question and that you actually asking for a PBEM how-to guide. In that case PashaDawg has once give me a thorough explanation of how to guide a PBEM game. I'll see if I can find it when I'm back home...
Currently we have possible three players, doesn't seem to promising for starting a game
