| mjd | Mime-encoded JDF |
| mjf | Magnet Field Job Data |
| mjk | Adobe Illustrator Mojikumi Set |
| mjm | JMF Mime Package |
| mjs | Mijas 7400 Costing Database |
| mjx | Objectif Lune Sugopita Data |
| mk2 | Flowcom 32 Data |
| mk4 | Akregator Data |
| mk4 | Schiller Medilog ECG Raw Data File |
| mkb | DVD Audio Media Key Block |
| mkc | MagicKey Currency Exchange Rate Data |
| mkd | Agilent ChemStation Multicell Kinetic Disk Data |
| mkd | Pervasive SQL Database |
| mke | Windows SDK Makefile |
| mkelem | IBM Rational ClearCase MKELEM Data |
| mkext | Mac OS X Mach Kernel Extension Cache |
| mkg | MokkAnnotator Mokkan Glass Data |
| mkh | WinMark Pro Mark Data |
| mkl | CAD6 Library |
| mklk | CyberLink MakeupDirector Look Data |
| mkn | PEARLNEQ MKN Input Data |
| mkr | my Knowledge Explorer Knowledge Representation |
| mkr | my Knowledge Representation Data |
| mks | MasterCook Cookbook Data |
| mks | TACT Data File |
| mku | MagicKey Units Definition |
| mkx | Diamino Fashion Suite File |
| mky | MagicKey Configuration Data |
| ml0 | MultiLedger Company Data |
| ml1 | MultiLedger Balance Data |
