| 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 |
| mysql | SQL Script |
| mz2 | Maze-Solver Data |
| mzd | Mozy Restore Definition Data |
| mzxml | SPC mzXML Data |
| m_p | Pro/ENGINEER Temporary Data |
