| 1 | M | Apple | Objective-C Implementation Format |
| 2 | M1S | N/A | MPEG-1 System Stream |
| 3 | M1V | N/A | MPEG-1 Video Format |
| 4 | M2 | Blizzard Entertainment | World Or Warcraft Model Object |
| 5 | M2A | N/A | MPEG-1 Layer 2 Audio Format |
|
| 6 | M2P | Moving Picture Experts Group | MPEG-2 Program Stream Format |
| 7 | M2R | N/A | Avaya Mib2Rules Perl Script |
| 8 | M2S | Maxthon | MPEG-2 Audio Video Format |
| 9 | M2T | N/A | MPEG-2 Transport Stream Format |
| 10 | M2TS | Sony | Blu-ray BDAV Video Format |
| 11 | M2V | N/A | MPEG-2 Video |
| 12 | M3G | Nokia | Mobile 3D Graphics Program |
| 13 | M3S | Ubisoft Entertainment S.A. | Myst III Exile Saved Game |
| 14 | M3T | Ubisoft Entertainment S.A. | Myst 3 Exile Text |
| 15 | M3U | Nullsoft | Media Playlist Format |
| 16 | M3U8 | Apple | UTF-8 M3U Playlist Format |
| 17 | M3URL | N/A | SMIL MP3 Playlist |
| 18 | M4 | N/A | Macro Processor Library |
| 19 | M4A | Apple | MPEG-4 Audio Format |
| 20 | M4B | Apple | MPEG-4 Audio Book Format |
| 21 | M4E | N/A | MPEG-4 Video Format |
| 22 | M4P | Apple | ITunes Music Store Audio Format |
| 23 | M4R | Apple | IPhone Ringtone Format |
| 24 | M4V | Apple | ITunes Video Format |
| 25 | M5M | N/A | Generic |
| 26 | M5P | MOTU | MachFive Preset File |
| 27 | M7A | MapKing International Limited | MapKing Map |
| 28 | M8 | Raven Software | Heretic II MipMap Image |
| 29 | MA | Autodesk | Maya Project Format |
| 30 | MAB | Mozilla | Mozilla Address Book |
| 31 | MAC | Apple | MacPaint Image |
| 32 | MACBIN | Apple | Macbinary Encoded Format |
| 33 | MACP | Apple, Inc. | Apple Macintosh MacPaint Bitmap Image |
| 34 | MAD | Microsoft | Access Module Shortcut |
| 35 | MAF | Microsoft | Microsoft Access Form Shortcut Format |
| 36 | MAFF | Mozilla | Mozilla Archive Format |
| 37 | MAGNET | N/A | Generic |
| 38 | MAILHOST | Microsoft | MSN Mailhost Settings Format |
| 39 | MAK | N/A | Makefile |
| 40 | MAKE | Apple | Xcode Makefile Script |
| 41 | MAKEFILE | N/A | Makefile |
| 42 | MAM | Microsoft | Microsoft Access Macro |
| 43 | MAML | Microsoft Corporation | Microsoft Assistance Markup Language |
| 44 | MAN | N/A | Unix Manual |
| 45 | MANIFEST | Microsoft | Windows Application Manifest Format |
| 46 | MAO | BioWare | Dragon Age Origins MAO XML |
| 47 | MAP | Pierre-Emmanuel Gougelet | Geographical Map Format |
| 48 | MAQ | Microsoft | Microsoft Access Query |
| 49 | MAR | Mozilla | Mozilla Archive |
| 50 | MARKDN | John Gruber | Markdown Format |
| 51 | MARKDOWN | John Gruber | Markdown Documentation Format |
| 52 | MARS | Adobe Systems | Adobe MARS Format |
| 53 | MAS | Microsoft | Microsoft Access Stored Procedures Format |
| 54 | MASTER | Microsoft | ASP.NET Master Page |
| 55 | MAT | Microsoft | Microsoft Access Table Shortcut Format |
| 56 | MATHML | N/A | Mathematical Markup Language |
| 57 | MATLAB | N/A | Matlab Script |
| 58 | MATPROJ | BioWare | Dragon Age Origins Material |
| 59 | MAV | Microsoft | Access View Format |
| 60 | MAW | Microsoft | Access Data Access Page |
| 61 | MAX | Autodesk | 3ds Max Scene Format |
| 62 | MAXFR | N/A | Generic |
| 63 | MB | Autodesk | Maya Binary Project Format |
| 64 | MBDB | Apple, Inc. | Apple IOS Backup Manifest |
| 65 | MBDX | Apple, Inc. | Apple IOS Backup Manifest |
| 66 | MBF | Microsoft | Microsoft Money Backup Format |
| 67 | MBM | Squad | Multi Bitmap Format |
| 68 | MBOX | N/A | E-mail Mailbox Format |
| 69 | MBS | Opera Software | Opera Mailbox Format |
| 70 | MBV | Victor Company of Japan, Ltd. | JVC Everio MediaBrowser Movie |
| 71 | MBX | Microsoft | Outlook Express Mailbox |
| 72 | MC6 | Smith Micro | Poser Material Collection Format |
| 73 | MCBN | N/A | Microsoft Excel 4 For Mac Chart |
| 74 | MCDB | Adobe Systems Incorporated | Adobe Premiere Pro Media Cache Database |
| 75 | MCI | N/A | Media Control Interface Format |
| 76 | MCL | Microsoft | Windows Media Center Link Format |
| 77 | MCML | Microsoft Corporation | Microsoft Windows Media Center MCML |
| 78 | MCUSW | Nokia Corporation | Nokia Mobile Phones With Symbian Firmware |
| 79 | MCX | CNC Software | MICRO CADAM-X/6000 Model Data Format |
| 80 | MD | John Gruber | Markdown Documentation Format |
| 81 | MD1 | N/A | GEAR CD/DVD Disc Image |
| 82 | MD2 | id Software | Quake 2 Player Model |
| 83 | MD3 | id Software | Quake 3 3D Model |
| 84 | MD4 | id Software LLC | Quake 3 MD4 Skeletal Model Format |
| 85 | MD5 | N/A | MD5 Checksum Format |
| 86 | MD5ANIM | id Software | Id Tech 4 Model Animation Format |
| 87 | MD5CAMERA | id Software | Id Tech 4 Model Camera Format |
| 88 | MD5MESH | id Software | Id Tech 4 3D Mesh Format |
| 89 | MD6MESH | N/A | id Tech 6 mesh |
| 90 | MDA | Microsoft | Access Add-in |
| 91 | MDB | Microsoft | Microsoft Access Database |
| 92 | MDBACKUP | Apple | IPhone Data Backup Format |
| 93 | MDBHTML | Microsoft | Microsoft Access Database HTML Format |
| 94 | MDC | Cognos | Image Minolta RD175 |
| 95 | MDDATA | Apple | IPhone Backup Format |
| 96 | MDE | Microsoft | Compiled Access Add-in Format |
| 97 | MDF | Alcohol Software | Media Disc Image Format |
| 98 | MDHTML | Microsoft Corporation | Microsoft Access HTML |
| 99 | MDINFO | Apple | IPhone Backup Information Format |
| 100 | MDL | Microsoft | Flight Simulator 95/98 3D Model Format |
| 101 | MDLE | N/A | Motion Description Language Extended |
| 102 | MDMP | Microsoft | Windows Minidump |
| 103 | MDN | N/A | Blank Access Database Template |
| 104 | MDOWN | John Gruber | Markdown Format |
| 105 | MDP | Microsoft | Visual C++ 5 Workspace Format |
| 106 | MDS | N/A | Media Descriptor Format |
| 107 | MDT | Intergraph | GeoMedia Access Database Template |
| 108 | MDTEXT | John Gruber | Markdown Markup Language |
| 109 | MDTXT | John Gruber | Markdown Markup Language |
| 110 | MDW | N/A | Access Workgroup Format |
| 111 | MDWN | John Gruber | Markdown Markup Language |
| 112 | MDX | DT Soft | Extended Media Descriptor Format |
| 113 | MDZ | N/A | Access Wizard Template |
| 114 | MEB | Ecru Software | PRO100 3D Interior Catalog Element |
| 115 | MED | RBF Software | Amiga MED Sound Format |
| 116 | MEDIAWIKI | N/A | Mediawiki Source |
| 117 | MEF | Mamiya | Mamiya RAW Image |
| 118 | MEH | N/A | Adobe Acrobat language resource |
| 119 | MEM | N/A | FoxPro Variable Format |
| 120 | MEMX | N/A | Generic |
| 121 | MENU | id Software | Quake 3 Engine Menu Format |
| 122 | MEQ | Corel Corporation | Corel WordPerfect Macro Editor Print Queue |
| 123 | MER | Corel Corporation | Corel WordPerfect Macro Editor Resident Area Format |
| 124 | MESH | Microsoft | DirectX Mesh Format |
| 125 | META4 | N/A | Metalink 4.0 |
| 126 | METADATA_NEVER_INDEX | Apple | Spotlight Never Index Format |
| 127 | METALINK | N/A | Metalink 3.0 |
| 128 | MEX | Insight Software Solutions | Macro Express Format |
| 129 | MF | Sun Microsystems | Java Manifest Format |
| 130 | MF1 | N/A | I-DEAS model |
| 131 | MF4 | Vector Informatik GmbH | Version 4.0 Measurement Data Format |
| 132 | MFA | Clickteam | Multimedia Fusion Development Format |
| 133 | MFIL | Blizzard Entertainment | Blizzard Software Update Format |
| 134 | MFL | Mozilla | Mozilla FastLoad Format |
| 135 | MFU | MobileFrame | Backdoor.Win32.Agent.mfu Virus Format |
| 136 | MFX | Clickteam | Multimedia Fusion Extension |
| 137 | MGA | Manga Reader | Manga Document |
| 138 | MGU | PG Music Inc. | Band-in-a-Box MIDI |
| 139 | MGX | Micrografx, Inc. | Micrografx Designer Drawing Format |
| 140 | MGZ | Konami Corporation | Metal Gear Solid Game Archive |
| 141 | MHA | N/A | MetaImage medical format |
| 142 | MHD | Bethesda Softworks LLC | Fallout 3 |
| 143 | MHL | N/A | Generic |
| 144 | MHT | N/A | MHTML Web Archive |
| 145 | MHTM | N/A | Mime HTML (MHTML) |
| 146 | MHTML | N/A | MIME HTML Format |
| 147 | MICRO | N/A | TeslaCrypt 3.0 Ransomware Encrypted File |
| 148 | MID | N/A | MIDI Format |
| 149 | MIDI | N/A | MIDI Format |
| 150 | MIF | Pitney Bowes Software | MapInfo Interchange Format |
| 151 | MIFF | ImageMagick Studio LLC | Magick Image |
| 152 | MIG | Microsoft | Windows Migration Backup Format |
| 153 | MIL | N/A | Micro Illustrator Uncompressed Image |
| 154 | MIM | Internet Engineering Task Force | Multi-Purpose Internet Mail Message Format |
| 155 | MIME | The Internet Engineering Task Force | Multi-Purpose Internet Mail Extension |
| 156 | MINDNODE | Markus Müller | MindNode Document |
| 157 | MINIGSF | Caitsith2 and Zoopd | Game Boy Advance Song File |
| 158 | MINISO | Fengtao Software Inc. | DVDFab Miniso Disk Image |
| 159 | MIR | Mini-Image Ripper | Mini-Image Ripper Disc Image |
| 160 | MIRO | N/A | Generic |
| 161 | MIS | GarageGames | Saved Game Mission Format |
| 162 | MIT | MineEdit | MineEdit Inventory Template Format |
| 163 | MIX | Microsoft | Microsoft Image Exchange Format |
| 164 | MJ2 | Joint Photographic Experts Group | Motion JPEG 2000 Video Clip |
| 165 | MJG | N/A | Trojan |
| 166 | MJP2 | N/A | JPEG 2000 Motion Sequence Format (ISO 15444-3) |
| 167 | MJPEG | N/A | Motion JPEG Video |
| 168 | MJPG | N/A | Motion JPEG Video Format |
| 169 | MJZ | N/A | Trojan.Win32.Agent.mjz |
| 170 | MK | N/A | Makefile |
| 171 | MK3D | Matroska | Matroska 3D Video Format |
| 172 | MKA | Matroska | Matroska Audio Format |
| 173 | MKDN | John Gruber | Markdown Markup Language |
| 174 | MKEXT | Apple, Inc. | Mac OS X Mach Kernel Extension Memory Cache |
| 175 | MKP | N/A | Cinestar Remote Control Configuration |
| 176 | MKS | VideoLAN Project Team | Matroska Subtitles Stream |
| 177 | MKT | Microsoft Corporation | Visual FoxPro Configuration |
| 178 | MKV | Matroska | Matroska Video Format |
| 179 | MKV3D | N/A | Matroska 3D Video Format |
| 180 | ML | Robin Milner | ML Source Code Format |
| 181 | MLC | Microsoft | Microsoft Language Interface Pack |
| 182 | MLOCATE | The GNOME Project | Gnome Desktop |
| 183 | MLY | N/A | OCaml Ocamlyacc Input |
| 184 | MM | FreeMind | Objective-C++ Source Format |
| 185 | MMAP | Mindjet | MindManager Map Format |
| 186 | MME | N/A | Multi-Purpose Internet Mail |
| 187 | MMF | Microsoft | Microsoft Mail Message Format |
| 188 | MMV | Sony | MicroMV Video Format |
| 189 | MN3 | Interplay Entertainment Corporation | Descent 3 Mission |
| 190 | MNFT | N/A | Generic |
| 191 | MNG | PNG Development Group | Multiple Network Graphic |
| 192 | MNO | Adobe Systems | Macromedia Design Note |
| 193 | MNY | Microsoft | Microsoft Money Format |
| 194 | MOB | MediaCorp | MOBTV Video Format |
| 195 | MOBI | Amazon | Mobipocket EBook |
| 196 | MOBILEBACKUPS | N/A | Apple macOS backup |
| 197 | MOBILECONFIG | Apple | Apple Mobile Configuration Format |
| 198 | MOBILEPROVISION | Apple | IOS Mobile Device Provisioning Profile Format |
| 199 | MOCHA | Adobe Systems Incorporated | Adobe Mocha For Adobe After Effects |
| 200 | MOD | Karsten Obarski | Amiga Music Module Format |
| 201 | MODEL | Dassault Systemes | CATIA 3D Model FIle |
| 202 | MODINFO | N/A | Civilization 5 mod information |
| 203 | MODUS | Adobe Systems Incorporated | Adobe Mocha For Adobe After Effects Modus |
| 204 | MOF | Desktop Management Task Force | Managed Object Format |
| 205 | MOGRT | Adobe Systems | Adobe Motion Graphics Template |
| 206 | MOI | N/A | JVC Everio Digital Audio Format |
| 207 | MOKEY | Adobe Systems Incorporated | Adobe Mocha For Adobe After Effects Mokey |
| 208 | MOL | Symyx Technologies | MDL Molfile |
| 209 | MONET | Adobe Systems Incorporated | Adobe Mocha For Adobe After Effects Monet |
| 210 | MONITORPANEL | Apple, Inc. | Apple Mac OS X Display Panel Extension |
| 211 | MOOV | Apple | Apple QuickTime Movie |
| 212 | MOPP | Havok Inc. | Havok Engine |
| 213 | MORSE | N/A | Ringtone Morse Code |
| 214 | MOS | Leaf Imaging | Leaf Camera RAW Format |
| 215 | MOT | NewTek | LightWave Motion Format |
| 216 | MOTOR | Adobe Systems Incorporated | Adobe Mocha For Adobe After Effects Motor |
| 217 | MOV | Apple | Apple QuickTime Movie |
| 218 | MOVIE | Apple | QuickTime Movie Format |
| 219 | MOXEL | Adobe Systems Incorporated | Adobe Mocha For Adobe After Effects Moxel |
| 220 | MOZ | N/A | Mozilla Cache Format |
| 221 | MOZ-BACKUP | Mozilla Corporation | Mozilla Backup |
| 222 | MOZCONFIG | N/A | Mozilla Firefox configuration data |
| 223 | MOZLZ4 | Mozilla | Compressed Firefox User Profile Data File |
| 224 | MP1 | N/A | MPEG-1 Layer 1 Audio Format |
| 225 | MP2 | Moving Picture Experts Group | MPEG Layer II Compressed Audio Format |
| 226 | MP2A | N/A | Sound Format (MPEG-1 Layer II Audio Stream) |
| 227 | MP2V | N/A | MPEG-2 Video Format |
| 228 | MP3 | Moving Picture Experts Group | MP3 Audio Format |
| 229 | MP3PRO | N/A | Generic |
| 230 | MP4 | Moving Picture Experts Group | MPEG-4 Video Format |
| 231 | MP41 | N/A | Microsoft MP41 video data |
| 232 | MP4A | Apple, Inc. | MPEG-4 MP4A Codec Audio |
| 233 | MP4V | Moving Picture Experts Group | MPEG-4 Video |
| 234 | MPA | N/A | MPEG-2 Audio Format |
| 235 | MPB | Franz Josef Wechselberger | MyPhoneExplorer Backup Format |
| 236 | MPC | Musepack | Musepack Compressed Audio Format |
| 237 | MPD | Microsoft | Microsoft Project Database |
| 238 | MPE | N/A | MPEG Movie Format |
| 239 | MPEG | Moving Picture Experts Group | MPEG Movie |
| 240 | MPEG1 | N/A | MPEG-1 Video Format |
| 241 | MPEG2 | Moving Picture Experts Group | Multiplexed MPEG-1/2 |
| 242 | MPEG4 | N/A | MPEG-4 Format |
| 243 | MPG | Moving Picture Experts Group | MPEG Video Format |
| 244 | MPG4 | Moving Picture Experts Group | MPEG-4 Video |
| 245 | MPGA | N/A | MPEG-1 Layer 3 Audio Format |
| 246 | MPGINDEX | Adobe Systems | Adobe MPEG Index Format |
| 247 | MPGV | N/A | MPEG-2 Video |
| 248 | MPGX | N/A | Generic |
| 249 | MPKG | N/A | Meta Package Format |
| 250 | MPL | Sony | AVCHD Playlist Format |
| 251 | MPLS | Blu-ray Disc Association | Blu-ray Movie Playlist Format |
| 252 | MPM | Corel Corporation | Corel WordPerfect MathPlan Macro Format |
| 253 | MPNT | Apple, Inc. | MacPaint Image Format |
| 254 | MPO | CIPA | Multi Picture Object Format |
| 255 | MPP | Microsoft | Microsoft Project Format |
| 256 | MPQ | Blizzard Entertainment, Inc. | Blizzard Entertainment Archive |
| 257 | MPQE | Blizzard Entertainment, Inc. | Blizzard Encrypted Game Data |
| 258 | MPS | Microsoft | Pocket Streets Map Format |
| 259 | MPT | Microsoft | Microsoft Project Template |
| 260 | MPV | Moving Picture Experts Group | MPEG Elementary Stream Video Format |
| 261 | MPV2 | N/A | MPEG-2 Video Stream |
| 262 | MPX | Microsoft | Microsoft Project Exchange Format |
| 263 | MQ | Microsoft | Message Queuing Message Log File |
| 264 | MQ5 | MetaQuotes Software | MQL5 Source Code File |
| 265 | MQH | MetaQuotes Software Corp. | MetaTrader Trading Terminal |
| 266 | MQV | Sony | Sony Movie Format |
| 267 | MRDB | N/A | Generic |
| 268 | MRES | N/A | Generic |
| 269 | MRF | Apple, Inc. | Macintosh Font |
| 270 | MRK | N/A | DPOF Auto Print Order Format |
| 271 | MRL | N/A | MRLR Multimedia Retrival Markup Language |
| 272 | MRQ | N/A | Generic |
| 273 | MRS | Corel Corporation | Corel WordPerfect Macro Resource Format |
| 274 | MRW | Minolta | Minolta Raw Image Format |
| 275 | MRXS | Carl Zeiss MicroImaging | MIRAX Virtual Slide Format |
| 276 | MS-TNEF | Microsoft | MS Transport Neutral Encapsulation Format |
| 277 | MS3D | Chumbalum Soft | MilkShape 3D Model |
| 278 | MSB | RITLabs SRL | The Bat! Format |
| 279 | MSC | Microsoft | Microsoft Management Console Snap-in Control Format |
| 280 | MSCX | The MuseScore Team | MuseScore Music Score Format |
| 281 | MSDL | N/A | Manchester Scene Description Language |
| 282 | MSDVD | Microsoft | Windows DVD Maker Project Format |
| 283 | MSG | Microsoft | Outlook Mail Message |
| 284 | MSH1XML | Microsoft | Monad Display Configuration File |
| 285 | MSH2 | N/A | Microsoft Shell script |
| 286 | MSH2XML | N/A | Windows PowerShell script |
| 287 | MSHA | Microsoft | Microsoft Help Asset Format |
| 288 | MSHC | Microsoft | Microsoft Help Container Format |
| 289 | MSHXML | Microsoft Corporation | Microsoft XML Typedata |
| 290 | MSI | Microsoft | Windows Installer Package |
| 291 | MSKIN | Maxthon International Limited | Maxthon Skin |
| 292 | MSLZ | N/A | Archive |
| 293 | MSM | Microsoft | Windows Installer Merge Module |
| 294 | MSMESSAGESTORE | Microsoft Corporation | Windows Mail Message Information Database |
| 295 | MSO | Microsoft | Inline E-mail Attachment |
| 296 | MSP | Microsoft | Windows Installer Patch |
| 297 | MSPDI | N/A | Microsoft Project XML data interchange |
| 298 | MSPX | Microsoft | Microsoft ASP.NET Web Page |
| 299 | MSRCINCIDENT | Microsoft | Windows Remote Assistance Invitation Format |
| 300 | MST | Microsoft | Windows Installer Setup Transform Format |
| 301 | MSU | Microsoft | Windows Vista Update Package |
| 302 | MSV | Sony | Memory Stick Voice Format |
| 303 | MSW | Microsoft | Microsoft Word 5 Document Format |
| 304 | MSWALLET | N/A | Microsoft Wallet item package |
| 305 | MSWD | Microsoft Corporation | Microsoft Word For Mac Document |
| 306 | MSWMM | Microsoft | Windows Movie Maker Project |
| 307 | MS_ | Microsoft Corporation | Microsoft Windows Winhelp Compressed |
| 308 | MTA | Samsung | Samsung AllShare Metadata Format |
| 309 | MTD | Musicnotes | Musicnotes Digital Sheet Music Format |
| 310 | MTF | Motorola | Motorola Theme Format |
| 311 | MTL | N/A | OBJ Material Format |
| 312 | MTM | N/A | MultiTracker Module |
| 313 | MTS | N/A | AVCHD Video Format |
| 314 | MTS1 | N/A | MPEG-2 Transport Stream |
| 315 | MTV | N/A | MTV Video Format |
| 316 | MTZ | MIUI | MIUI Theme |
| 317 | MU | Corel Corporation | Corel Quattro Pro For DOS Menu Definition Format |
| 318 | MU3 | Myriad Software | Myriad Packed Musical Score |
| 319 | MUI | Microsoft | Multilingual User Interface Format |
| 320 | MULIB | Adobe Systems Incorporated | Adobe Muse Exported Library |
| 321 | MUM | Microsoft | Windows Vista Update Package |
| 322 | MUS | MakeMusic | Finale Notation Format |
| 323 | MUSE | Adobe Systems | Adobe Muse Website Project |
| 324 | MVB | N/A | Multimedia Viewer Book Source Format |
| 325 | MVD | MAGIX | Movie Edit Pro Movie Format |
| 326 | MVD2 | N/A | Generic |
| 327 | MVDX | MatchWare A/S | MindView MindMap Archive |
| 328 | MVE | BioWare | Infinity Engine Movie Format |
| 329 | MVF | Autodesk, Inc. | AutoFlix Stop Frame |
| 330 | MVG | ImageMagick Studio LLC | ImageMagick Proprietary Vector Graphics Format |
| 331 | MVI | Autodesk | AutoCAD Movie Command Format |
| 332 | MW | Maplesoft | Maple Worksheet |
| 333 | MWD | Mariner Software | MarinerWrite Document |
| 334 | MX1 | N/A | Coucoucircus.org Audio Temporary |
| 335 | MX2 | ValuSoft | MasterCook Recipe |
| 336 | MXE | Corel Corporation | Corel Quattro Pro Startup Macro Format |
| 337 | MXF | SMPTE | Material Exchange Format |
| 338 | MXI | Adobe | Adobe Dreamweaver Extension Manager Format |
| 339 | MXL | The MuseScore Team | Compressed MusicXML Format |
| 340 | MXML | Adobe Systems | Flex MXML Component |
| 341 | MXP | Adobe Systems | Adobe Extension Package |
| 342 | MXSD | IBM | IBM WebSphere Message Definition |
| 343 | MYD | MySQL | MySQL Database Data Format |
| 344 | MYI | Oracle | MySQL MyISAM Index Format |
| 345 | MYOB | MYOB Limited | MYOB Data |
| 346 | MYR | Myriad Software | Myriad Music Format |
| 347 | MYSQL | N/A | MySQL data |
| 348 | MZZ | Microsoft | Microsoft .NET Download Package |
