Can you pass files so players can take there turns on separate computers?

Not in a smooth manner, it is one of the first RTS-games. It is mainly local multiplayer

The best chance of remote multiplayer would be setting up the disk image with retroach-dosbox core and netplay.

You could teorethically use a dosbox version with savestates if you REALLY need to pass files, but I do not think that is what you are after.

This seemingly "officially licensed" version (below) may be what you're looking for. It seems to be actively developed also.

It offers both local multiplayer, or online (Internet) multiplayer. I'm not sure yet if that local means LAN, or ONLY on the same computer. But the 'Online Multiplayer' feature probably covers the needs of LAN multiplayer as well (which is what I'm assuming you're asking about).

MULEonline
dot
com

It is officially licensed. It's mentioned on the site of the current Ozark Softscape as such (it's been down for a few months now for whatever reason, but you can find it on the Wayback Machine). Ozark is run by Dani's children (mainly Melanie I think). They are the ones who licensed/permitted M.U.L.E. Returns, Planet M.U.L.E., the board-game and all the Ozark Softscape published releases on GOG.