| mqo | Metasequoia Object File |
| mqp | Metasequoia Palette File |
| mqtbx | XTRF Terminology Database |
| mqu | GraphicUSB Capture Data |
| mqx | Malete Query Access File |
| mqxliff | memoQ XLIFF Data |
| mr | Mapped Read Format Data |
| mrd | Malete Record Data File |
| mre | Steinberg MR Editor File |
| mrec | MADRIX Record File |
| mrf | Mapped Read Format Data |
| mrg | MySQL Merge File |
| mrk | Kodak EasyShare Job Definition |
| mrk | GP-Pro EX Mark Library |
| mrk | Pro/ENGINEER Markup File |
| mrm | CloseToSoftware MacroRunner Macro |
| mrp | Xilinx MAP Report |
| mrpd | IBM TS3500 Machine Reported Product Data |
| mrt | Stimulsoft Report |
| mrv | Marvin Document Format File |
| mrx | Malete Record Access File |
| ms | Autodesk 3D Studio Max Script |
| ms-tnef | MS Transport Neutral Encapsulation Format |
| ms1 | Crux MS/MS Data |
| ms2 | Crux MS/MS Data |
| ms4 | MAILERS+4 Index Data |
| msbcm | Microsoft Office Business Contact Manager Backup Data |
| msbt | Nintendo Wii Galaxy Dialogue Data |
| mscc | mSecure Data |
| mscml | Media Server Control Markup Language File |
| mscx | mSecure Backup |
| msd | Map Service Definition |
| mse-installer | Magic Set Editor Installer |
| msecure | mSecure Data |
| msf | Miranda IM Skin |