| mwl | Mighty Draw Windows Library |
| mx | Mathematica Serialized Package |
| mxad | Mandelbrot Explorer All Data |
| mxaddon | Maxthon Browser Add-On |
| mxc | ArcVIEW Geocode Coverage ODB Index |
| mxc2 | MAGIX Thumbnail Cache |
| mxcs | Mandelbrot Explorer Color Scheme |
| mxd | ArcMAP Document |
| mxdic | Maxthon Browser Dictionary |
| mxdl | Maxthon Browser Incomplete Download File |
| mxe | Macro Express Playable Macro |
| mxfd | Abbyy eFormFiller Form File |
| mxfr | Mandelbrot Explorer Fractal Region Data |
| mxg | Miinoto Exchangeable Group |
| mxit | MXit Data |
| mxm | Maxwell Render Material |
| mxn | MultiNote Exchangeable Notes |
| mxprj | NI Maschine Project |
| mxq | SA Chess MXQ Data |
| mxr | MatrixREDUCE 2.0 PSAM XML Format Data |
| mxrw | Mandelbrot Explorer RAW Data |
| mxs | ArcVIEW Geocode ODB Index |
| mxskin | Maxthon Browser Skin |
| mxt | Fortran 5 Data File |
| my3d | Hasbro My3D File |
| myb | MYOB AccountRight Company Data |
| mybible | MySword Bible Database |
| mycolors | Stardock MyColors Theme |
| myd | MySQL MyISAM Table Data |
| mye | MYOB AccountEdge Exported Data |
| myi | MySQL MyISAM Table Index Data |
| mym | Mymenuify Theme Data |
| myo | MYOB AccountRight Company Data |
| myob | MYOB AccountRight Company Data |
| myox | MYOB AccountRight 2011 Company Data |