I'm serving with user made MP maps. Does everyone who wants to join have to have these maps, too?

OFP clients download from the server machine on-the-fly copies of maps that the client computer is missing. Keep in mind that more time is needed for the download to complete before the game can begin. The larger the map files, the longer the game start delay.

Where are these on-the-fly maps downloaded to? It depends:

• For OFP versions up to 1.4x, the on-the-fly map PBO files were downloaded into OFP's MPMISSIONS subdirectory.
   
• For OFP: Resistance version 1.75, on-the-fly MP maps are downloaded into OFP's TMP subdirectory, in order to avoid overwriting missions that might exist with the same file names in the MPMISSIONS subdirectory. As its name implies, TMP is a temporary file folder. If you want to save on-the-fly MP maps in OFP: Resistance version 1.75, you'll have to ALT+TAB out of Resistance and manually save them.
   
• For OFP: Resistance version 1.85 and above, on-the-fly MP map copies are now saved to a new subdirectory, MpmissionsCache. The difference between the MpmissionsCache subdirectory and the previous use of the TMP subdirectory is that now, downloaded map files are not deleted, and therefore are not downloaded again when playing the same map, unless of course, the map has since been changed. OFP's MP code is cleaver enough to make a file checksum comparison between the cached copy and the one currently on the server side. If checksums don't match, a new copy of the map is downloaded to replace the currently cached copy in the MpmissionsCache subdirectory.