| message | WebSTAR Directory Indexer Message |
| meta | Apache META File |
| meta4 | Metalink Data |
| metadata | Acronis True Image Metadata |
| metadix | Apertium Metadix Dictionary Data |
| metalink | Metalink Data |
| metriclog | Apple iOS Diagnostic Data |
| mets | METS Data |
| mev | TIGR MultiExperiment Viewer Format Data |
| mew | MultiEdit Encoded Status Data |
| mex | Macro Express Macro File |
| mex | MAXQDA Exchange Data |
| mexp | MetaMorph NX Experiment Data |
| mf4 | ASAM Measurement Data Format File |
| mfalist | Ashampoo Photo Commander Slideshow List |
| mfasl | Mozilla Fastload File |
| mfc | CMUSphinx Features Data |
| mfcc | HTK Mel-Frequency Cepstral Coefficient Data |
| mfd | Multiframe Design |
| mfe | MobileFrame Enterprise Data |
| mff | EGI Metafile Format Data |
| mfg | PTC Creo Manufacturing Process Data |
| mfil | World of Warcraft Software Update |
| mfj | MOBCAL Input Data |
| mfl | ModFit LT Analysis Report |
| mfl | Mozilla Fastload File |
| mfn | MODFLOW Name Dataset |
| mfr | Moldflow Result |
| mfs | MetFS Encrypted File System |
| mfst | Symantec Endpoint Protection Definitions Manifest Data |
| mftpkg | MacFamilyTree Project Package |
| mg | MetaGuide Setup Data |
| mgc | Media Catalog MGC File |
| mgc | Equation Illustrator Main Data File |
| mgd | Master Grade Data |