| m2l | Maxthon 2 Language Pack |
| m2p | Maxthon 2 Browser Plugin |
| m2p | GROMACS Mat2PS Data |
| m2s | Maxthon 2 Browser Skin |
| m3d | DJ Mix Pro Database |
| m3r | Autodesk Moldflow 3D Fill+Pack Restart File |
| m4d | Sage MAS 90 Data File |
| m4i | IBM Voice Type Languages Newuser Data |
| m4p | Sage MAS 90 Program File |
| m4t | Sage MAS 90 Table File |
| m64 | Mupen64 Movie Capture |
| m77t | GEODAS MGD77T Data |
| m7a | MapKing Map Data |
| m99 | MicroStation Modification User Resource File |
| maa | MMANA Antenna Data |
| mab | Mozilla Address Book |
| mac | SmartWare Macro File |
| mac | PATCHMASTER Macro File |
| macbin | Macbinary Encoded |
| mad | Microsoft Access Module Shortcut |
| mail | NeoPlanet Mail Data |
| main | FileMaker Pro Dictionary Data |
| mamp | MAMP Related Data |
| map | TECkit Mapping Table |
| map | Map Data |
| map | WAsP Terrain Map |
| maplet | Maple Maplet File |
| mapx | MapDotNet UX Map File |
| marshal | Marshal Data Migration Model |
| mask | Adobe SpeedGrade Color Mask |
| material | Rigs of Rods Texture Reference |
| math | AnalyticMath Data |
| mauve | Mauve Alignment Data |
| maxc | Autodesk 3D Studio MAX Container |
| maxd | PaperPort Annotation Data |
