This is my quick class for determining the MimeType of a file by its extension.  It is very basic.  Please post more types if I am missing them so I can keep it updated.   using System.Collections.Generic; namespace Lara.Sys { public class MimeTypes { public Dictionary<string,string> AllTypes; public string GetMimeType(string extension) { if (AllTypes.ContainsKey(extension)) return AllTypes[extension]; else return "text/plain"; } public MimeTypes() { AllTypes = new Dictionary<string,string>(); AllTypes.Add(".3dm","x-world/x-3dmf"); AllTypes.Add(".3dmf","x-world/x-3dmf"); AllTypes.Add(".a","application/octet-stream"); AllTypes.Add(".aab","application/x-authorware-bin"); AllTypes.Add(".aam","application/x-authorware-map"); AllTypes.Add(".aas","application/x-authorware-seg"); AllTypes.Add(".abc","text/vnd.abc"); AllTypes.Add(".acgi","text/html"); AllTypes.Add(".afl","video/animaflex"); AllTypes.Add(".ai","application/postscript"); AllTypes.Add(".aif","audio/aiff"); AllTypes.Add(".aifc","audio/aiff"); AllTypes.Add(".aiff","audio/aiff"); AllTypes.Add(".aim","application/x-aim"); AllTypes.Add(".aip","text/x-audiosoft-intra"); AllTypes.Add(".ani","application/x-navi-animation"); AllTypes.Add(".aos","application/x-nokia-9000-communicator-add-on-software"); AllTypes.Add(".aps","application/mime"); AllTypes.Add(".arc","application/octet-stream"); AllTypes.Add(".arj","application/arj"); AllTypes.Add(".art","image/x-jg"); AllTypes.Add(".asf","video/x-ms-asf"); AllTypes.Add(".asm","text/x-asm"); AllTypes.Add(".asp","text/asp"); AllTypes.Add(".asx","video/x-ms-asf"); AllTypes.Add(".au","audio/basic"); AllTypes.Add(".avi","video/avi"); AllTypes.Add(".avs","video/avs-video"); AllTypes.Add(".bcpio","application/x-bcpio"); AllTypes.Add(".bin","application/octet-stream"); AllTypes.Add(".bm","image/bmp"); AllTypes.Add(".bmp","image/bmp"); AllTypes.Add(".boo","application/book"); AllTypes.Add(".book","application/book"); AllTypes.Add(".boz","application/x-bzip2"); AllTypes.Add(".bsh","application/x-bsh"); AllTypes.Add(".bz","application/x-bzip"); AllTypes.Add(".bz2","application/x-bzip2"); AllTypes.Add(".c","text/plain"); AllTypes.Add(".c++","text/plain"); AllTypes.Add(".cat","application/vnd.ms-pki.seccat"); AllTypes.Add(".cc","text/plain"); AllTypes.Add(".ccad","application/clariscad"); AllTypes.Add(".cco","application/x-cocoa"); AllTypes.Add(".cdf","application/cdf"); AllTypes.Add(".cer","application/x-x509-ca-cert"); AllTypes.Add(".cha","application/x-chat"); AllTypes.Add(".chat","application/x-chat"); AllTypes.Add(".class","application/java"); AllTypes.Add(".com","application/octet-stream"); AllTypes.Add(".conf","text/plain"); AllTypes.Add(".cpio","application/x-cpio"); AllTypes.Add(".cpp","text/x-c"); AllTypes.Add(".cpt","application/x-compactpro"); AllTypes.Add(".crl","application/pkix-crl"); AllTypes.Add(".crt","application/x-x509-ca-cert"); AllTypes.Add(".csh","application/x-csh"); AllTypes.Add(".css","text/css"); AllTypes.Add(".cxx","text/plain"); AllTypes.Add(".dcr","application/x-director"); AllTypes.Add(".deepv","application/x-deepv"); AllTypes.Add(".def","text/plain"); AllTypes.Add(".dif","video/x-dv"); AllTypes.Add(".dir","application/x-director"); AllTypes.Add(".dl","video/dl"); AllTypes.Add(".doc","application/msword"); AllTypes.Add(".dot","application/msword"); AllTypes.Add(".dp","application/commonground"); AllTypes.Add(".drw","application/drafting"); AllTypes.Add(".dump","application/octet-stream"); AllTypes.Add(".dv","video/x-dv"); AllTypes.Add(".dvi","application/x-dvi"); AllTypes.Add(".dwf","model/vnd.dwf"); AllTypes.Add(".dwg","image/x-dwg"); AllTypes.Add(".dxf","application/dxf"); AllTypes.Add(".dxr","application/x-director"); AllTypes.Add(".el","text/x-script.elisp"); AllTypes.Add(".elc","application/x-elc"); AllTypes.Add(".env","application/x-envoy"); AllTypes.Add(".eps","application/postscript"); AllTypes.Add(".es","application/x-esrehber"); AllTypes.Add(".etx","text/x-setext"); AllTypes.Add(".evy","application/envoy"); AllTypes.Add(".exe","application/octet-stream"); AllTypes.Add(".f","text/plain"); AllTypes.Add(".f77","text/x-fortran"); AllTypes.Add(".f90","text/plain"); AllTypes.Add(".fdf","application/vnd.fdf"); AllTypes.Add(".fif","image/fif"); AllTypes.Add(".fli","video/fli"); AllTypes.Add(".flo","image/florian"); AllTypes.Add(".flx","text/vnd.fmi.flexstor"); AllTypes.Add(".fmf","video/x-atomic3d-feature"); AllTypes.Add(".for","text/plain"); AllTypes.Add(".fpx","image/vnd.fpx"); AllTypes.Add(".frl","application/freeloader"); AllTypes.Add(".funk","audio/make"); AllTypes.Add(".g","text/plain"); AllTypes.Add(".g3","image/g3fax"); AllTypes.Add(".gif","image/gif"); AllTypes.Add(".gl","video/gl"); AllTypes.Add(".gsd","audio/x-gsm"); AllTypes.Add(".gsm","audio/x-gsm"); AllTypes.Add(".gsp","application/x-gsp"); AllTypes.Add(".gss","application/x-gss"); AllTypes.Add(".gtar","application/x-gtar"); AllTypes.Add(".gz","application/x-gzip"); AllTypes.Add(".gzip","application/x-gzip"); AllTypes.Add(".h","text/plain"); AllTypes.Add(".hdf","application/x-hdf"); AllTypes.Add(".help","application/x-helpfile"); AllTypes.Add(".hgl","application/vnd.hp-hpgl"); AllTypes.Add(".hh","text/plain"); AllTypes.Add(".hlb","text/x-script"); AllTypes.Add(".hlp","application/hlp"); AllTypes.Add(".hpg","application/vnd.hp-hpgl"); AllTypes.Add(".hpgl","application/vnd.hp-hpgl"); AllTypes.Add(".hqx","application/binhex"); AllTypes.Add(".hta","application/hta"); AllTypes.Add(".htc","text/x-component"); AllTypes.Add(".htm","text/html"); AllTypes.Add(".html","text/html"); AllTypes.Add(".htmls","text/html"); AllTypes.Add(".htt","text/webviewhtml"); AllTypes.Add(".htx","text/html"); AllTypes.Add(".ice","x-conference/x-cooltalk"); AllTypes.Add(".ico","image/x-icon"); AllTypes.Add(".idc","text/plain"); AllTypes.Add(".ief","image/ief"); AllTypes.Add(".iefs","image/ief"); AllTypes.Add(".iges","application/iges"); AllTypes.Add(".igs","application/iges"); AllTypes.Add(".ima","application/x-ima"); AllTypes.Add(".imap","application/x-httpd-imap"); AllTypes.Add(".inf","application/inf"); AllTypes.Add(".ins","application/x-internett-signup"); AllTypes.Add(".ip","application/x-ip2"); AllTypes.Add(".isu","video/x-isvideo"); AllTypes.Add(".it","audio/it"); AllTypes.Add(".iv","application/x-inventor"); AllTypes.Add(".ivr","i-world/i-vrml"); AllTypes.Add(".ivy","application/x-livescreen"); AllTypes.Add(".jam","audio/x-jam"); AllTypes.Add(".jav","text/plain"); AllTypes.Add(".java","text/plain"); AllTypes.Add(".jcm","application/x-java-commerce"); AllTypes.Add(".jfif","image/jpeg"); AllTypes.Add(".jfif-tbnl","image/jpeg"); AllTypes.Add(".jpe","image/jpeg"); AllTypes.Add(".jpeg","image/jpeg"); AllTypes.Add(".jpg","image/jpeg"); AllTypes.Add(".jps","image/x-jps"); AllTypes.Add(".js","application/x-javascript"); AllTypes.Add(".jut","image/jutvision"); AllTypes.Add(".kar","music/x-karaoke"); AllTypes.Add(".ksh","application/x-ksh"); AllTypes.Add(".la","audio/nspaudio"); AllTypes.Add(".lam","audio/x-liveaudio"); AllTypes.Add(".latex","application/x-latex"); AllTypes.Add(".lha","application/octet-stream"); AllTypes.Add(".lhx","application/octet-stream"); AllTypes.Add(".list","text/plain"); AllTypes.Add(".lma","audio/nspaudio"); AllTypes.Add(".log","text/plain"); AllTypes.Add(".lsp","application/x-lisp"); AllTypes.Add(".lst","text/plain"); AllTypes.Add(".lsx","text/x-la-asf"); AllTypes.Add(".ltx","application/x-latex"); AllTypes.Add(".lzh","application/octet-stream"); AllTypes.Add(".lzx","application/octet-stream"); AllTypes.Add(".m","text/plain"); AllTypes.Add(".m1v","video/mpeg"); AllTypes.Add(".m2a","audio/mpeg"); AllTypes.Add(".m2v","video/mpeg"); AllTypes.Add(".m3u","audio/x-mpequrl"); AllTypes.Add(".m4a", "video/x-m4a"); AllTypes.Add(".m4v", "video/x-m4v"); AllTypes.Add(".man","application/x-troff-man"); AllTypes.Add(".map","application/x-navimap"); AllTypes.Add(".mar","text/plain"); AllTypes.Add(".mbd","application/mbedlet"); AllTypes.Add(".mc$","application/x-magic-cap-package-1.0"); AllTypes.Add(".mcd","application/mcad"); AllTypes.Add(".mcf","text/mcf"); AllTypes.Add(".mcp","application/netmc"); AllTypes.Add(".me","application/x-troff-me"); AllTypes.Add(".mht","message/rfc822"); AllTypes.Add(".mhtml","message/rfc822"); AllTypes.Add(".mid","audio/midi"); AllTypes.Add(".midi","audio/midi"); AllTypes.Add(".mif","application/x-frame"); AllTypes.Add(".mime","www/mime"); AllTypes.Add(".mjf","audio/x-vnd.audioexplosion.mjuicemediafile"); AllTypes.Add(".mjpg","video/x-motion-jpeg"); AllTypes.Add(".mm","application/base64"); AllTypes.Add(".mme","application/base64"); AllTypes.Add(".mod","audio/mod"); AllTypes.Add(".moov","video/quicktime"); AllTypes.Add(".mov","video/quicktime"); AllTypes.Add(".movie","video/x-sgi-movie"); AllTypes.Add(".mp2","audio/mpeg"); AllTypes.Add(".mp3","audio/mpeg3"); AllTypes.Add(".mp4","video/mp4"); AllTypes.Add(".mpa","audio/mpeg"); AllTypes.Add(".mpc","application/x-project"); AllTypes.Add(".mpe","video/mpeg"); AllTypes.Add(".mpeg","video/mpeg"); AllTypes.Add(".mpg","audio/mpeg"); AllTypes.Add(".mpga","audio/mpeg"); AllTypes.Add(".mpp","application/vnd.ms-project"); AllTypes.Add(".mpt","application/x-project"); AllTypes.Add(".mpv","application/x-project"); AllTypes.Add(".mpx","application/x-project"); AllTypes.Add(".mrc","application/marc"); AllTypes.Add(".ms","application/x-troff-ms"); AllTypes.Add(".mv","video/x-sgi-movie"); AllTypes.Add(".my","audio/make"); AllTypes.Add(".mzz","application/x-vnd.audioexplosion.mzz"); AllTypes.Add(".nap","image/naplps"); AllTypes.Add(".naplps","image/naplps"); AllTypes.Add(".nc","application/x-netcdf"); AllTypes.Add(".ncm","application/vnd.nokia.configuration-message"); AllTypes.Add(".nif","image/x-niff"); AllTypes.Add(".niff","image/x-niff"); AllTypes.Add(".nix","application/x-mix-transfer"); AllTypes.Add(".nsc","application/x-conference"); AllTypes.Add(".nvd","application/x-navidoc"); AllTypes.Add(".o","application/octet-stream"); AllTypes.Add(".oda","application/oda"); AllTypes.Add(".omc","application/x-omc"); AllTypes.Add(".omcd","application/x-omcdatamaker"); AllTypes.Add(".omcr","application/x-omcregerator"); AllTypes.Add(".p","text/x-pascal"); AllTypes.Add(".p10","application/pkcs10"); AllTypes.Add(".p12","application/pkcs-12"); AllTypes.Add(".p7a","application/x-pkcs7-signature"); AllTypes.Add(".p7c","application/pkcs7-mime"); AllTypes.Add(".p7m","application/pkcs7-mime"); AllTypes.Add(".p7r","application/x-pkcs7-certreqresp"); AllTypes.Add(".p7s","application/pkcs7-signature"); AllTypes.Add(".part","application/pro_eng"); AllTypes.Add(".pas","text/pascal"); AllTypes.Add(".pbm","image/x-portable-bitmap"); AllTypes.Add(".pcl","application/x-pcl"); AllTypes.Add(".pct","image/x-pict"); AllTypes.Add(".pcx","image/x-pcx"); AllTypes.Add(".pdb","chemical/x-pdb"); AllTypes.Add(".pdf","application/pdf"); AllTypes.Add(".pfunk","audio/make"); AllTypes.Add(".pgm","image/x-portable-graymap"); AllTypes.Add(".pic","image/pict"); AllTypes.Add(".pict","image/pict"); AllTypes.Add(".pkg","application/x-newton-compatible-pkg"); AllTypes.Add(".pko","application/vnd.ms-pki.pko"); AllTypes.Add(".pl","text/plain"); AllTypes.Add(".plx","application/x-pixclscript"); AllTypes.Add(".pm","image/x-xpixmap"); AllTypes.Add(".pm4","application/x-pagemaker"); AllTypes.Add(".pm5","application/x-pagemaker"); AllTypes.Add(".png","image/png"); AllTypes.Add(".pnm","application/x-portable-anymap"); AllTypes.Add(".pot","application/mspowerpoint"); AllTypes.Add(".pov","model/x-pov"); AllTypes.Add(".ppa","application/vnd.ms-powerpoint"); AllTypes.Add(".ppm","image/x-portable-pixmap"); AllTypes.Add(".pps","application/mspowerpoint"); AllTypes.Add(".ppt","application/powerpoint"); AllTypes.Add(".ppz","application/mspowerpoint"); AllTypes.Add(".pre","application/x-freelance"); AllTypes.Add(".prt","application/pro_eng"); AllTypes.Add(".ps","application/postscript"); AllTypes.Add(".psd","application/octet-stream"); AllTypes.Add(".pvu","paleovu/x-pv"); AllTypes.Add(".pwz","application/vnd.ms-powerpoint"); AllTypes.Add(".py","text/x-script.phyton"); AllTypes.Add(".pyc","applicaiton/x-bytecode.python"); AllTypes.Add(".qcp","audio/vnd.qcelp"); AllTypes.Add(".qd3","x-world/x-3dmf"); AllTypes.Add(".qd3d","x-world/x-3dmf"); AllTypes.Add(".qif","image/x-quicktime"); AllTypes.Add(".qt","video/quicktime"); AllTypes.Add(".qtc","video/x-qtc"); AllTypes.Add(".qti","image/x-quicktime"); AllTypes.Add(".qtif","image/x-quicktime"); AllTypes.Add(".ra","audio/x-realaudio"); AllTypes.Add(".ram","audio/x-pn-realaudio"); AllTypes.Add(".ras","image/cmu-raster"); AllTypes.Add(".rast","image/cmu-raster"); AllTypes.Add(".rexx","text/x-script.rexx"); AllTypes.Add(".rf","image/vnd.rn-realflash"); AllTypes.Add(".rgb","image/x-rgb"); AllTypes.Add(".rm","application/vnd.rn-realmedia"); AllTypes.Add(".rmi","audio/mid"); AllTypes.Add(".rmm","audio/x-pn-realaudio"); AllTypes.Add(".rmp","audio/x-pn-realaudio"); AllTypes.Add(".rng","application/ringing-tones"); AllTypes.Add(".rnx","application/vnd.rn-realplayer"); AllTypes.Add(".roff","application/x-troff"); AllTypes.Add(".rp","image/vnd.rn-realpix"); AllTypes.Add(".rpm","audio/x-pn-realaudio-plugin"); AllTypes.Add(".rt","text/richtext"); AllTypes.Add(".rtf","application/rtf"); AllTypes.Add(".rtx","application/rtf"); AllTypes.Add(".rv","video/vnd.rn-realvideo"); AllTypes.Add(".s","text/x-asm"); AllTypes.Add(".s3m","audio/s3m"); AllTypes.Add(".saveme","application/octet-stream"); AllTypes.Add(".sbk","application/x-tbook"); AllTypes.Add(".scm","video/x-scm"); AllTypes.Add(".sdml","text/plain"); AllTypes.Add(".sdp","application/sdp"); AllTypes.Add(".sdr","application/sounder"); AllTypes.Add(".sea","application/sea"); AllTypes.Add(".set","application/set"); AllTypes.Add(".sgm","text/sgml"); AllTypes.Add(".sgml","text/sgml"); AllTypes.Add(".sh","application/x-sh"); AllTypes.Add(".shar","application/x-shar"); AllTypes.Add(".shtml","text/html"); AllTypes.Add(".sid","audio/x-psid"); AllTypes.Add(".sit","application/x-sit"); AllTypes.Add(".skd","application/x-koan"); AllTypes.Add(".skm","application/x-koan"); AllTypes.Add(".skp","application/x-koan"); AllTypes.Add(".skt","application/x-koan"); AllTypes.Add(".sl","application/x-seelogo"); AllTypes.Add(".smi","application/smil"); AllTypes.Add(".smil","application/smil"); AllTypes.Add(".snd","audio/basic"); AllTypes.Add(".sol","application/solids"); AllTypes.Add(".spc","text/x-speech"); AllTypes.Add(".spl","application/futuresplash"); AllTypes.Add(".spr","application/x-sprite"); AllTypes.Add(".sprite","application/x-sprite"); AllTypes.Add(".src","application/x-wais-source"); AllTypes.Add(".ssi","text/x-server-parsed-html"); AllTypes.Add(".ssm","application/streamingmedia"); AllTypes.Add(".sst","application/vnd.ms-pki.certstore"); AllTypes.Add(".step","application/step"); AllTypes.Add(".stl","application/sla"); AllTypes.Add(".stp","application/step"); AllTypes.Add(".sv4cpio","application/x-sv4cpio"); AllTypes.Add(".sv4crc","application/x-sv4crc"); AllTypes.Add(".svf","image/vnd.dwg"); AllTypes.Add(".svr","application/x-world"); AllTypes.Add(".swf","application/x-shockwave-flash"); AllTypes.Add(".t","application/x-troff"); AllTypes.Add(".talk","text/x-speech"); AllTypes.Add(".tar","application/x-tar"); AllTypes.Add(".tbk","application/toolbook"); AllTypes.Add(".tcl","application/x-tcl"); AllTypes.Add(".tcsh","text/x-script.tcsh"); AllTypes.Add(".tex","application/x-tex"); AllTypes.Add(".texi","application/x-texinfo"); AllTypes.Add(".texinfo","application/x-texinfo"); AllTypes.Add(".text","text/plain"); AllTypes.Add(".tgz","application/x-compressed"); AllTypes.Add(".tif","image/tiff"); AllTypes.Add(".tiff","image/tiff"); AllTypes.Add(".tr","application/x-troff"); AllTypes.Add(".tsi","audio/tsp-audio"); AllTypes.Add(".tsp","audio/tsplayer"); AllTypes.Add(".tsv","text/tab-separated-values"); AllTypes.Add(".turbot","image/florian"); AllTypes.Add(".txt","text/plain"); AllTypes.Add(".uil","text/x-uil"); AllTypes.Add(".uni","text/uri-list"); AllTypes.Add(".unis","text/uri-list"); AllTypes.Add(".unv","application/i-deas"); AllTypes.Add(".uri","text/uri-list"); AllTypes.Add(".uris","text/uri-list"); AllTypes.Add(".ustar","application/x-ustar"); AllTypes.Add(".uu","application/octet-stream"); AllTypes.Add(".uue","text/x-uuencode"); AllTypes.Add(".vcd","application/x-cdlink"); AllTypes.Add(".vcs","text/x-vcalendar"); AllTypes.Add(".vda","application/vda"); AllTypes.Add(".vdo","video/vdo"); AllTypes.Add(".vew","application/groupwise"); AllTypes.Add(".viv","video/vivo"); AllTypes.Add(".vivo","video/vivo"); AllTypes.Add(".vmd","application/vocaltec-media-desc"); AllTypes.Add(".vmf","application/vocaltec-media-file"); AllTypes.Add(".voc","audio/voc"); AllTypes.Add(".vos","video/vosaic"); AllTypes.Add(".vox","audio/voxware"); AllTypes.Add(".vqe","audio/x-twinvq-plugin"); AllTypes.Add(".vqf","audio/x-twinvq"); AllTypes.Add(".vql","audio/x-twinvq-plugin"); AllTypes.Add(".vrml","application/x-vrml"); AllTypes.Add(".vrt","x-world/x-vrt"); AllTypes.Add(".vsd","application/x-visio"); AllTypes.Add(".vst","application/x-visio"); AllTypes.Add(".vsw","application/x-visio"); AllTypes.Add(".w60","application/wordperfect6.0"); AllTypes.Add(".w61","application/wordperfect6.1"); AllTypes.Add(".w6w","application/msword"); AllTypes.Add(".wav","audio/wav"); AllTypes.Add(".wb1","application/x-qpro"); AllTypes.Add(".wbmp","image/vnd.wap.wbmp"); AllTypes.Add(".web","application/vnd.xara"); AllTypes.Add(".wiz","application/msword"); AllTypes.Add(".wk1","application/x-123"); AllTypes.Add(".wmf","windows/metafile"); AllTypes.Add(".wml","text/vnd.wap.wml"); AllTypes.Add(".wmlc","application/vnd.wap.wmlc"); AllTypes.Add(".wmls","text/vnd.wap.wmlscript"); AllTypes.Add(".wmlsc","application/vnd.wap.wmlscriptc"); AllTypes.Add(".word","application/msword"); AllTypes.Add(".wp","application/wordperfect"); AllTypes.Add(".wp5","application/wordperfect"); AllTypes.Add(".wp6","application/wordperfect"); AllTypes.Add(".wpd","application/wordperfect"); AllTypes.Add(".wq1","application/x-lotus"); AllTypes.Add(".wri","application/mswrite"); AllTypes.Add(".wrz","model/vrml"); AllTypes.Add(".wsc","text/scriplet"); AllTypes.Add(".wsrc","application/x-wais-source"); AllTypes.Add(".wtk","application/x-wintalk"); AllTypes.Add(".xbm","image/xbm"); AllTypes.Add(".xdr","video/x-amt-demorun"); AllTypes.Add(".xgz","xgl/drawing"); AllTypes.Add(".xif","image/vnd.xiff"); AllTypes.Add(".xl","application/excel"); AllTypes.Add(".xla","application/excel"); AllTypes.Add(".xlb","application/excel"); AllTypes.Add(".xlc","application/excel"); AllTypes.Add(".xld","application/excel"); AllTypes.Add(".xlk","application/excel"); AllTypes.Add(".xll","application/excel"); AllTypes.Add(".xlm","application/excel"); AllTypes.Add(".xls","application/excel"); AllTypes.Add(".xlt","application/excel"); AllTypes.Add(".xlv","application/excel"); AllTypes.Add(".xlw","application/excel"); AllTypes.Add(".xm","audio/xm"); AllTypes.Add(".xml","text/xml"); AllTypes.Add(".xmz","xgl/movie"); AllTypes.Add(".xpix","application/x-vnd.ls-xpix"); AllTypes.Add(".xpm","image/xpm"); AllTypes.Add(".x-png","image/png"); AllTypes.Add(".xsr","video/x-amt-showrun"); AllTypes.Add(".xwd","image/x-xwd"); AllTypes.Add(".xyz","chemical/x-pdb"); AllTypes.Add(".z","application/x-compressed"); AllTypes.Add(".zip","application/x-compressed"); AllTypes.Add(".zoo","application/octet-stream"); AllTypes.Add(".zsh","text/x-script.zsh"); } } }