Have them create empire files and email them to you. You then use them to create a game. In the mechanics tab, select Simultaneous Movement and Different Machines. Add a Savegame name. Then, email the game file to all players. They play their turns and email their .plr files to you. You use them to load the game as host and process the turns.
I would suggest that you use
PBW instead. It automates most of this for you.