| 231. | .mwii | Text document (MacWrite II) |
| 232. | .mwp | SmartMaster (Lotus Word Pro) |
| 233. | .mx | Common matrix routines (Matlab) ◊ Linker information (Modula-3) |
| 234. | .mx3 | Dynamically linked subroutines (80386/486 MS-Windows) (Matlab) |
| 235. | .mxc | geocoding index for read-write coverages (ODB format) (ArcView) |
| 236. | .mxd | Map file (ArcInfo) |
| 237. | .mxl | Support file (PackRat 5.0) |
| 238. | .mxm | Mail file (Microsoft Project) ◊ MathConnex Module |
| 239. | .mxs | geocoding index for read-write shapefiles (ODB format) (ArcView) |
| 240. | .mxt | Data (Microsoft C) |