MIME[多用途網際網路郵件擴展類型]

MIME(Multipurpose Internet Mail Extensions)多用途網際網路郵件擴展類型。是設定某種擴展名的檔案用一種應用程式來打開的方式類型，當該擴展名檔案被訪問的時候，瀏覽器會自動使用指定應用程式來打開。多用於指定一些客戶端自定義的檔案名稱，以及一些媒體檔案打開方式。

它是一個網際網路標準，擴展了電子郵件標準，使其能夠支持：

非ASCII字元文本；非文本格式附屬檔案（二進制、聲音、圖像等）；由多部分（multiple parts）組成的訊息體；包含非ASCII字元的頭信息（Header information）。

這個標準被定義在RFC 2045、RFC 2046、RFC 2047、RFC 2048、RFC 2049等RFC中。 MIME改善了由RFC 822轉變而來的RFC 2822，這些舊標準規定電子郵件標準並不允許在郵件訊息中使用7位ASCII字元集以外的字元。正因如此，一些非英語字元訊息和二進制檔案，圖像，聲音等非文字訊息原本都不能在電子郵件中傳輸(MIME可以)。MIME規定了用於表示各種各樣的數據類型的符號化方法。 此外，在全球資訊網中使用的HTTP協定中也使用了MIME的框架，標準被擴展為網際網路媒體類型。

背景介紹

多用途網際網路郵件擴展，它是一個網際網路標準，在1992年最早套用於電子郵件系統，但後來也套用到瀏覽器。伺服器會將它們傳送的多媒體數據的類型告訴瀏覽器，而通知手段就是說明該多媒體數據的MIME類型，從而讓瀏覽器知道接收到的信息哪些是MP3檔案，哪些是Shockwave檔案等等。伺服器將MIME標誌符放入傳送的數據中來告訴瀏覽器使用哪種外掛程式讀取相關檔案。

MIME能夠支持非ASCII字元、二進制格式附屬檔案等多種格式的郵件訊息。這個標準被定義在RFC 2045，RFC 2046，RFC 2047，RFC 2048，RFC 2049等RFC中。 由RFC 822轉變而來的RFC 2822，規定電子郵件標準並不允許在郵件訊息中使用7位ASCII字元集以外的字元。正因如此，一些非英語字元訊息和二進制檔案，圖像，聲音等非文字訊息都不能在電子郵件中傳輸。MIME規定了用於表示各種各樣的數據類型的符號化方法。

瀏覽器接收到檔案後，會進入外掛程式系統進行查找，查找出哪種外掛程式可以識別讀取接收到的檔案。如果瀏覽器不清楚調用哪種外掛程式系統，它可能會告訴用戶缺少某外掛程式，或者直接選擇某現有外掛程式來試圖讀取接收到的檔案，或者可能會導致系統的崩潰。傳輸的信息中缺少MIME標識可能導致的情況很難估計，因為某些計算機系統可能不會出現什麼故障，但某些計算機可能就會因此而崩潰。

檢查一個伺服器是否正確設定了MIME類型的步驟是：

在Netscape瀏覽器中打開伺服器網頁。

進入"Tools"選單，選擇"Page Info"。

在彈出的視窗中點擊上層框架中的"EMBED"。

在下層框架中查看MIME的類型是否為"application/x-director"或"application/x-shockwave-flash"，如果是上述信息的話表明伺服器已經正確設定了MIME類型；而如果MIME類型列出的是文本內容、八位一組的數據或是其它形式均表明伺服器的MIME類型沒有設定正確。

如果伺服器沒有正確標明其傳送的數據的類型，伺服器管理員應該正確添加相關信息，具體操作方法非常簡單快捷。

Microsoft公司套用於Windows系統下的瀏覽器使用ActiveX控制項，而不是Netscape外掛程式，這種瀏覽器不必象其它瀏覽器那樣依靠MIME的編碼。"OBJECT"標籤的"CLSID"屬性準確地標明了應調用哪種程式來讀取接收到的檔案，因此瀏覽器不必象"EMBED"標籤那樣選擇一種讀取程式。正因為如此，你往往會在使用帶外掛程式的瀏覽器時遇到MIME問題，而使用ActiveX控制項的瀏覽器則很少出現此類麻煩。

正由於上述工作方式的差別也解釋了一種現象，不知你是否發現在使用Netscape瀏覽器播放WAV檔案時，瀏覽器會調用LiveConnect外掛程式進行播放，而其它瀏覽器一般都使用通用的QuickTime的播放外掛程式等來進行播放，這是因為Netscape瀏覽器接收檔案需要讀取MIME標識符，以便決定調用哪種程式來讀取接收的檔案，而伺服器設定在Netscape瀏覽器中播放WAV檔案應使用LiveConnect外掛程式，因此Netscape瀏覽器接收到WAV格式的檔案時必然就會調用LiveConnect外掛程式，但由於其它瀏覽器不使用這種方式，因此它們都使用系統默認的播放WAV格式檔案的播放器。當然Flash電影檔案並不存在這種問題，因為只有Flash播放器才能夠正確讀取這種格式的檔案。

在把輸出結果傳送到瀏覽器上的時候，瀏覽器必須啟動適當的應用程式來處理這個輸出文檔。這可以通過多種類型MIME（多功能網際郵件擴充協定）來完成。在HTTP中，MIME類型被定義在Content-Type header中。

例如，假設你要傳送一個Microsoft Excel檔案到客戶端。那么這時的MIME類型就是“excel”。在大多數實際情況中，這個檔案然後將傳送給Excel來處理（假設我們設定Excel為處理特殊MIME類型的應用程式）。在ASP中，設定MIME類型的方法是通過Response對象的ContentType屬性。

檔案格式

最早的HTTP協定中，並沒有附加的數據類型信息，所有傳送的數據都被客戶程式解釋為超文本標記語言HTML 文檔，而為了支持多媒體數據類型，HTTP協定中就使用了附加在文檔之前的MIME數據類型信息來標識數據類型。

MIME意為多功能Internet郵件擴展，它設計的最初目的是為了在傳送電子郵件時附加多媒體數據，讓郵件客戶程式能根據其類型進行處理。然而當它被HTTP協定支持之後，它的意義就更為顯著了。它使得HTTP傳輸的不僅是普通的文本，而變得豐富多彩。

每個MIME類型由兩部分組成，前面是數據的大類別，例如聲音audio、圖象image等，後面定義具體的種類。

常見的MIME類型(通用型)：

超文本標記語言文本 .html text/html

xml文檔 .xml text/xml

XHTML文檔 .xhtml application/xhtml+xml

普通文本 .txt text/plain

RTF文本 .rtf application/rtf

PDF文檔 .pdf application/pdf

Microsoft Word檔案 .word application/msword

PNG圖像 .png image/png

GIF圖形 .gif image/gif

JPEG圖形 .jpeg,.jpg image/jpeg

au聲音檔案 .au audio/basic

MIDI音樂檔案 mid,.midi audio/midi,audio/x-midi

RealAudio音樂檔案 .ra, .ram audio/x-pn-realaudio

MPEG檔案 .mpg,.mpeg video/mpeg

AVI檔案 .avi video/x-msvideo

GZIP檔案 .gz application/x-gzip

TAR檔案 .tar application/x-tar

任意的二進制數據 application/octet-stream

用於 WAP 伺服器 的MIME類型有：
MRP檔案（國內普遍的手機）	.mrp application/octet-stream
IPA檔案(IPHONE)	.ipa application/iphone-package-archive
	.deb application/x-debian-package-archive
APK檔案(安卓系統)	.apk application/vnd.android.package-archive
CAB檔案(Windows Mobile)	.cab application/vnd.cab-com-archive
XAP檔案(Windows Phone 7)	.xap application/x-silverlight-app
SIS檔案(symbian平台/S60V1)	.sis application/vnd.symbian.install-archive *（下有）
SISX檔案(symbian平台/S60V3/V5)	.sisx application/vnd.symbian.epoc/x-sisx-app
JAR、JAD檔案(JAVA平台手機通用格式)	.jar .jad下面有

Internet中有一個專門組織IANA來確認標準的MIME類型，但Internet發展的太快，很多應用程式等不及IANA來確認他們使用的MIME類型為標準類型。因此他們使用在類別中以x-開頭的方法標識這個類別還沒有成為標準，例如：x-gzip，x-tar等。事實上這些類型運用的很廣泛，已經成為了事實標準。只要客戶機和伺服器共同承認這個MIME類型，即使它是不標準的類型也沒有關係，客戶程式就能根據MIME類型，採用具體的處理手段來處理數據。而Web伺服器和瀏覽器（包括作業系統）中，預設都設定了標準的和常見的MIME類型，只有對於不常見的 MIME類型，才需要同時設定伺服器和客戶瀏覽器，以進行識別。

由於MIME類型與文檔的後綴相關，因此伺服器使用文檔的後綴來區分不同檔案的MIME類型，伺服器中必須定義文檔後綴和MIME類型之間的對應關係。而客戶程式從伺服器上接收數據的時候，它只是從伺服器接受數據流，並不了解文檔的名字，因此伺服器必須使用附加信息來告訴客戶程式數據的MIME類型。伺服器在傳送真正的數據之前，就要先傳送標誌數據的MIME類型的信息，這個信息使用Content-type關鍵字進行定義，例如對於HTML文檔，伺服器將首先傳送以下兩行MIME標識信息,這個標識並不是真正的數據檔案的一部分。

Content-type: text/html

注意，第二行為一個空行，這是必須的，使用這個空行的目的是將MIME信息與真正的數據內容分隔開。

MIME利用了一個事實就是，RFC 822在訊息體的內容中做了一點限制：唯一的限制就是只能使用簡單的ASCII文本。所以，MIME信息由正常的Internet文本郵件組成，文本郵件擁有一些特別的符合RFC 822的信息頭和格式化過的信息體（用ASCII 的子集來表示的附屬檔案）。這些MIME頭給出了一種在郵件中表示附屬檔案的特別的方法。

信息剖析

一個普通的文本郵件的信息包含一個頭部分（To: From: Subject: 等等）和一個體部分（Hello Mr.,等等）。在一個符合MIME的信息中，也包含一個信息頭並不奇怪，郵件的各個部分叫做MIME段，每段前也綴以一個特別的頭。MIME郵件只是基於RFC 822郵件的一個擴展，然而它有著自己的RFC規範集。

頭欄位

MIME頭根據在郵件包中的位置，大體上分為MIME信息頭和MIME段頭。（譯者：MIME信息頭指整個郵件的頭，而MIME段頭只每個MIME段的頭。）

MIME信息頭有：

MIME-Version:

這個頭提供了所用MIME的版本號。這個值習慣上為1.0。

Content-Type:

它定義了數據的類型，以便數據能被適當的處理。有效的類型有：text，image，audio，video，applications，multipart和message。注意任何一個二進制附屬檔案都應該被叫做application/octet- stream。這個頭的一些用例為：image/jpg, application/mswork，multipart/mixed，這只是很少的一部分。

Content-Transfer-Encoding:

這是所有頭中最重要的一個，因為它說明了對數據所執行的編碼方式，客戶/MUA 將用它對附屬檔案進行解碼。對於每個附屬檔案，可以使用7bit，8bit，binary ，quoted-printable，base64和custom中的一種編碼方式。7bit編碼是用在US ASCII字元集上的常用的一種編碼方式，也就是，保持它的原樣。8bit和binary編碼一般不用。對人類可讀的標準文本，如果傳輸要經過對格式有影響的網關時對其進行保護，可以使用quoted printable 。Base64是一種通用方法，在需要決定使用哪一種編碼方法時，它提供了一個不用費腦子的選擇；它通常用在二進制，非文本數據上。注意，任何非7bit 數據必須用一種模式編碼，這樣它就可以通過Internet郵件網關！

Content-ID:

如果Content-Type是message/external-body或multipart/alternative時，這個頭就有用了，它超出了本文的範圍。

Content-Description:

這是一個可選的頭。它是任何信息段內容的自由文本描述。描述必須使用us-ascii碼。

Content-Disposition:

一個試驗性的頭，它用於給客戶程式/MUA提供提示，來決定是否在行內顯示附屬檔案或作為單獨的附屬檔案。

MIME段頭（出現在實際的MIME附屬檔案部分的頭），除了MIME-Version頭，可以擁有以上任何頭欄位。如果一個MIME頭是信息塊的一部分，它將作用於整個信息體。例如，如果Content-Transfer-Encoding顯示在信息（指整個信息）頭中，它套用於整個信息體，但是如果它顯示在一個MIME段里，它"只能"用於那個段中。

注意：其可以對自動對收到的郵件進行解密。

類型大全

格式前面為後輟名，後面為對應的MIME型（例如：rar application/x-rar-compressed 表示。RAR對應的是application/x-rar-compressed ）

{ ".323", "text/h323" },

{ ".3gp", "video/3gpp" },

{ ".aab", "application/x-authoware-bin" },

{ ".aam", "application/x-authoware-map" },

{ ".aas", "application/x-authoware-seg" },

{ ".acx", "application/internet-property-stream" },

{ ".ai", "application/postscript" },

{ ".aif", "audio/x-aiff" },

{ ".aifc", "audio/x-aiff" },

{ ".aiff", "audio/x-aiff" },

{ ".als", "audio/X-Alpha5" },

{ ".amc", "application/x-mpeg" },

{ ".ani", "application/octet-stream" },

{ ".apk", "application/vnd.android.package-archive" },

{ ".asc", "text/plain" },

{ ".asd", "application/astound" },

{ ".asf", "video/x-ms-asf" },

{ ".asn", "application/astound" },

{ ".asp", "application/x-asap" },

{ ".asr", "video/x-ms-asf" },

{ ".asx", "video/x-ms-asf" },

{ ".au", "audio/basic" },

{ ".avb", "application/octet-stream" },

{ ".avi", "video/x-msvideo" },

{ ".awb", "audio/amr-wb" },

{ ".axs", "application/olescript" },

{ ".bas", "text/plain" },

{ ".bcpio", "application/x-bcpio" },

{ ".bin ", "application/octet-stream" },

{ ".bld", "application/bld" },

{ ".bld2", "application/bld2" },

{ ".bmp", "image/bmp" },

{ ".bpk", "application/octet-stream" },

{ ".bz2", "application/x-bzip2" },

{ ".c", "text/plain" },

{ ".cal", "image/x-cals" },

{ ".cat", "application/vnd.ms-pkiseccat" },

{ ".ccn", "application/x-cnc" },

{ ".cco", "application/x-cocoa" },

{ ".cdf", "application/x-cdf" },

{ ".cer", "application/x-x509-ca-cert" },

{ ".cgi", "magnus-internal/cgi" },

{ ".chat", "application/x-chat" },

{ ".class", "application/octet-stream" },

{ ".clp", "application/x-msclip" },

{ ".cmx", "image/x-cmx" },

{ ".co", "application/x-cult3d-object" },

{ ".cod", "image/cis-cod" },

{ ".conf", "text/plain" },

{ ".cpio", "application/x-cpio" },

{ ".cpp", "text/plain" },

{ ".cpt", "application/mac-compactpro" },

{ ".crd", "application/x-mscardfile" },

{ ".crl", "application/pkix-crl" },

{ ".crt", "application/x-x509-ca-cert" },

{ ".csh", "application/x-csh" },

{ ".csm", "chemical/x-csml" },

{ ".csml", "chemical/x-csml" },

{ ".css", "text/css" },

{ ".cur", "application/octet-stream" },

{ ".dcm", "x-lml/x-evm" },

{ ".dcr", "application/x-director" },

{ ".dcx", "image/x-dcx" },

{ ".der", "application/x-x509-ca-cert" },

{ ".dhtml", "text/html" },

{ ".dir", "application/x-director" },

{ ".dll", "application/x-msdownload" },

{ ".dmg", "application/octet-stream" },

{ ".dms", "application/octet-stream" },

{ ".doc", "application/msword" },

{ ".docx", "application/vnd.openxmlformats-officedocument.wordprocessingml.document" },

{ ".dot", "application/msword" },

{ ".dvi", "application/x-dvi" },

{ ".dwf", "drawing/x-dwf" },

{ ".dwg", "application/x-autocad" },

{ ".dxf", "application/x-autocad" },

{ ".dxr", "application/x-director" },

{ ".ebk", "application/x-expandedbook" },

{ ".emb", "chemical/x-embl-dl-nucleotide" },

{ ".embl", "chemical/x-embl-dl-nucleotide" },

{ ".eps", "application/postscript" },

{ ".epub", "application/epub+zip" },

{ ".eri", "image/x-eri" },

{ ".es", "audio/echospeech" },

{ ".esl", "audio/echospeech" },

{ ".etc", "application/x-earthtime" },

{ ".etx", "text/x-setext" },

{ ".evm", "x-lml/x-evm" },

{ ".evy", "application/envoy" },

{ ".exe", "application/octet-stream" },

{ ".fh4", "image/x-freehand" },

{ ".fh5", "image/x-freehand" },

{ ".fhc", "image/x-freehand" },

{ ".fif", "application/fractals" },

{ ".flr", "x-world/x-vrml" },

{ ".flv", "flv-application/octet-stream" },

{ ".fm", "application/x-maker" },

{ ".fpx", "image/x-fpx" },

{ ".fvi", "video/isivideo" },

{ ".gau", "chemical/x-gaussian-input" },

{ ".gca", "application/x-gca-compressed" },

{ ".gdb", "x-lml/x-gdb" },

{ ".gif", "image/gif" },

{ ".gps", "application/x-gps" },

{ ".gtar", "application/x-gtar" },

{ ".gz", "application/x-gzip" },

{ ".h", "text/plain" },

{ ".hdf", "application/x-hdf" },

{ ".hdm", "text/x-hdml" },

{ ".hdml", "text/x-hdml" },

{ ".hlp", "application/winhlp" },

{ ".hqx", "application/mac-binhex40" },

{ ".hta", "application/hta" },

{ ".htc", "text/x-component" },

{ ".htm", "text/html" },

{ ".html", "text/html" },

{ ".hts", "text/html" },

{ ".htt", "text/webviewhtml" },

{ ".ice", "x-conference/x-cooltalk" },

{ ".ico", "image/x-icon" },

{ ".ief", "image/ief" },

{ ".ifm", "image/gif" },

{ ".ifs", "image/ifs" },

{ ".iii", "application/x-iphone" },

{ ".imy", "audio/melody" },

{ ".ins", "application/x-internet-signup" },

{ ".ips", "application/x-ipscript" },

{ ".ipx", "application/x-ipix" },

{ ".isp", "application/x-internet-signup" },

{ ".it", "audio/x-mod" },

{ ".itz", "audio/x-mod" },

{ ".ivr", "i-world/i-vrml" },

{ ".j2k", "image/j2k" },

{ ".jad", "text/vnd.sun.j2me.app-descriptor" },

{ ".jam", "application/x-jam" },

{ ".jar", "application/java-archive" },

{ ".java", "text/plain" },

{ ".jfif", "image/pipeg" },

{ ".jnlp", "application/x-java-jnlp-file" },

{ ".jpe", "image/jpeg" },

{ ".jpeg", "image/jpeg" },

{ ".jpg", "image/jpeg" },

{ ".jpz", "image/jpeg" },

{ ".js", "application/x-javascript" },

{ ".jwc", "application/jwc" },

{ ".kjx", "application/x-kjx" },

{ ".lak", "x-lml/x-lak" },

{ ".latex", "application/x-latex" },

{ ".lcc", "application/fastman" },

{ ".lcl", "application/x-digitalloca" },

{ ".lcr", "application/x-digitalloca" },

{ ".lgh", "application/lgh" },

{ ".lha", "application/octet-stream" },

{ ".lml", "x-lml/x-lml" },

{ ".lmlpack", "x-lml/x-lmlpack" },

{ ".log", "text/plain" },

{ ".lsf", "video/x-la-asf" },

{ ".lsx", "video/x-la-asf" },

{ ".lzh", "application/octet-stream" },

{ ".m13", "application/x-msmediaview" },

{ ".m14", "application/x-msmediaview" },

{ ".m15", "audio/x-mod" },

{ ".m3u", "audio/x-mpegurl" },

{ ".m3url", "audio/x-mpegurl" },

{ ".m4a", "audio/mp4a-latm" },

{ ".m4b", "audio/mp4a-latm" },

{ ".m4p", "audio/mp4a-latm" },

{ ".m4u", "video/vnd.mpegurl" },

{ ".m4v", "video/x-m4v" },

{ ".ma1", "audio/ma1" },

{ ".ma2", "audio/ma2" },

{ ".ma3", "audio/ma3" },

{ ".ma5", "audio/ma5" },

{ ".man", "application/x-troff-man" },

{ ".map", "magnus-internal/imagemap" },

{ ".mbd", "application/mbedlet" },

{ ".mct", "application/x-mascot" },

{ ".mdb", "application/x-msaccess" },

{ ".mdz", "audio/x-mod" },

{ ".me", "application/x-troff-me" },

{ ".mel", "text/x-vmel" },

{ ".mht", "message/rfc822" },

{ ".mhtml", "message/rfc822" },

{ ".mi", "application/x-mif" },

{ ".mid", "audio/mid" },

{ ".midi", "audio/midi" },

{ ".mif", "application/x-mif" },

{ ".mil", "image/x-cals" },

{ ".mio", "audio/x-mio" },

{ ".mmf", "application/x-skt-lbs" },

{ ".mng", "video/x-mng" },

{ ".mny", "application/x-msmoney" },

{ ".moc", "application/x-mocha" },

{ ".mocha", "application/x-mocha" },

{ ".mod", "audio/x-mod" },

{ ".mof", "application/x-yumekara" },

{ ".mol", "chemical/x-mdl-molfile" },

{ ".mop", "chemical/x-mopac-input" },

{ ".mov", "video/quicktime" },

{ ".movie", "video/x-sgi-movie" },

{ ".mp2", "video/mpeg" },

{ ".mp3", "audio/mpeg" },

{ ".mp4", "video/mp4" },

{ ".mpa", "video/mpeg" },

{ ".mpc", "application/vnd.mpohun.certificate" },

{ ".mpe", "video/mpeg" },

{ ".mpeg", "video/mpeg" },

{ ".mpg", "video/mpeg" },

{ ".mpg4", "video/mp4" },

{ ".mpga", "audio/mpeg" },

{ ".mpn", "application/vnd.mophun.application" },

{ ".mpp", "application/vnd.ms-project" },

{ ".mps", "application/x-mapserver" },

{ ".mpv2", "video/mpeg" },

{ ".mrl", "text/x-mrml" },

{ ".mrm", "application/x-mrm" },

{ ".ms", "application/x-troff-ms" },

{ ".msg", "application/vnd.ms-outlook" },

{ ".mts", "application/metastream" },

{ ".mtx", "application/metastream" },

{ ".mtz", "application/metastream" },

{ ".mvb", "application/x-msmediaview" },

{ ".mzv", "application/metastream" },

{ ".nar", "application/zip" },

{ ".nbmp", "image/nbmp" },

{ ".nc", "application/x-netcdf" },

{ ".ndb", "x-lml/x-ndb" },

{ ".ndwn", "application/ndwn" },

{ ".nif", "application/x-nif" },

{ ".nmz", "application/x-scream" },

{ ".nokia-op-logo", "image/vnd.nok-oplogo-color" },

{ ".npx", "application/x-netfpx" },

{ ".nsnd", "audio/nsnd" },

{ ".nva", "application/x-neva1" },

{ ".nws", "message/rfc822" },

{ ".oda", "application/oda" },

{ ".ogg", "audio/ogg" },

{ ".oom", "application/x-AtlasMate-Plugin" },

{ ".p10", "application/pkcs10" },

{ ".p12", "application/x-pkcs12" },

{ ".p7b", "application/x-pkcs7-certificates" },

{ ".p7c", "application/x-pkcs7-mime" },

{ ".p7m", "application/x-pkcs7-mime" },

{ ".p7r", "application/x-pkcs7-certreqresp" },

{ ".p7s", "application/x-pkcs7-signature" },

{ ".pac", "audio/x-pac" },

{ ".pae", "audio/x-epac" },

{ ".pan", "application/x-pan" },

{ ".pbm", "image/x-portable-bitmap" },

{ ".pcx", "image/x-pcx" },

{ ".pda", "image/x-pda" },

{ ".pdb", "chemical/x-pdb" },

{ ".pdf", "application/pdf" },

{ ".pfr", "application/font-tdpfr" },

{ ".pfx", "application/x-pkcs12" },

{ ".pgm", "image/x-portable-graymap" },

{ ".pict", "image/x-pict" },

{ ".pko", "application/ynd.ms-pkipko" },

{ ".pm", "application/x-perl" },

{ ".pma", "application/x-perfmon" },

{ ".pmc", "application/x-perfmon" },

{ ".pmd", "application/x-pmd" },

{ ".pml", "application/x-perfmon" },

{ ".pmr", "application/x-perfmon" },

{ ".pmw", "application/x-perfmon" },

{ ".png", "image/png" },

{ ".pnm", "image/x-portable-anymap" },

{ ".pnz", "image/png" },

{ ".pot,", "application/vnd.ms-powerpoint" },

{ ".ppm", "image/x-portable-pixmap" },

{ ".pps", "application/vnd.ms-powerpoint" },

{ ".ppt", "application/vnd.ms-powerpoint" },

{ ".pptx", "application/vnd.openxmlformats-officedocument.presentationml.presentation" },

{ ".pqf", "application/x-cprplayer" },

{ ".pqi", "application/cprplayer" },

{ ".prc", "application/x-prc" },

{ ".prf", "application/pics-rules" },

{ ".prop", "text/plain" },

{ ".proxy", "application/x-ns-proxy-autoconfig" },

{ ".ps", "application/postscript" },

{ ".ptlk", "application/listenup" },

{ ".pub", "application/x-mspublisher" },

{ ".pvx", "video/x-pv-pvx" },

{ ".qcp", "audio/vnd.qcelp" },

{ ".qt", "video/quicktime" },

{ ".qti", "image/x-quicktime" },

{ ".qtif", "image/x-quicktime" },

{ ".r3t", "text/vnd.rn-realtext3d" },

{ ".ra", "audio/x-pn-realaudio" },

{ ".ram", "audio/x-pn-realaudio" },

{ ".rar", "application/octet-stream" },

{ ".ras", "image/x-cmu-raster" },

{ ".rc", "text/plain" },

{ ".rdf", "application/rdf+xml" },

{ ".rf", "image/vnd.rn-realflash" },

{ ".rgb", "image/x-rgb" },

{ ".rlf", "application/x-richlink" },

{ ".rm", "audio/x-pn-realaudio" },

{ ".rmf", "audio/x-rmf" },

{ ".rmi", "audio/mid" },

{ ".rmm", "audio/x-pn-realaudio" },

{ ".rmvb", "audio/x-pn-realaudio" },

{ ".rnx", "application/vnd.rn-realplayer" },

{ ".roff", "application/x-troff" },

{ ".rp", "image/vnd.rn-realpix" },

{ ".rpm", "audio/x-pn-realaudio-plugin" },

{ ".rt", "text/vnd.rn-realtext" },

{ ".rte", "x-lml/x-gps" },

{ ".rtf", "application/rtf" },

{ ".rtg", "application/metastream" },

{ ".rtx", "text/richtext" },

{ ".rv", "video/vnd.rn-realvideo" },

{ ".rwc", "application/x-rogerwilco" },

{ ".s3m", "audio/x-mod" },

{ ".s3z", "audio/x-mod" },

{ ".sca", "application/x-supercard" },

{ ".scd", "application/x-msschedule" },

{ ".sct", "text/scriptlet" },

{ ".sdf", "application/e-score" },

{ ".sea", "application/x-stuffit" },

{ ".setpay", "application/set-payment-initiation" },

{ ".setreg", "application/set-registration-initiation" },

{ ".sgm", "text/x-sgml" },

{ ".sgml", "text/x-sgml" },

{ ".sh", "application/x-sh" },

{ ".shar", "application/x-shar" },

{ ".shtml", "magnus-internal/parsed-html" },

{ ".shw", "application/presentations" },

{ ".si6", "image/si6" },

{ ".si7", "image/vnd.stiwap.sis" },

{ ".si9", "image/vnd.lgtwap.sis" },

{ ".sis", "application/vnd.symbian.install" },

{ ".sit", "application/x-stuffit" },

{ ".skd", "application/x-Koan" },

{ ".skm", "application/x-Koan" },

{ ".skp", "application/x-Koan" },

{ ".skt", "application/x-Koan" },

{ ".slc", "application/x-salsa" },

{ ".smd", "audio/x-smd" },

{ ".smi", "application/smil" },

{ ".smil", "application/smil" },

{ ".smp", "application/studiom" },

{ ".smz", "audio/x-smd" },

{ ".snd", "audio/basic" },

{ ".spc", "application/x-pkcs7-certificates" },

{ ".spl", "application/futuresplash" },

{ ".spr", "application/x-sprite" },

{ ".sprite", "application/x-sprite" },

{ ".sdp", "application/sdp" },

{ ".spt", "application/x-spt" },

{ ".src", "application/x-wais-source" },

{ ".sst", "application/vnd.ms-pkicertstore" },

{ ".stk", "application/hyperstudio" },

{ ".stl", "application/vnd.ms-pkistl" },

{ ".stm", "text/html" },

{ ".svg", "image/svg+xml" },

{ ".sv4cpio", "application/x-sv4cpio" },

{ ".sv4crc", "application/x-sv4crc" },

{ ".svf", "image/vnd" },

{ ".svg", "image/svg+xml" },

{ ".svh", "image/svh" },

{ ".svr", "x-world/x-svr" },

{ ".swf", "application/x-shockwave-flash" },

{ ".swfl", "application/x-shockwave-flash" },

{ ".t", "application/x-troff" },

{ ".tad", "application/octet-stream" },

{ ".talk", "text/x-speech" },

{ ".tar", "application/x-tar" },

{ ".taz", "application/x-tar" },

{ ".tbp", "application/x-timbuktu" },

{ ".tbt", "application/x-timbuktu" },

{ ".tcl", "application/x-tcl" },

{ ".tex", "application/x-tex" },

{ ".texi", "application/x-texinfo" },

{ ".texinfo", "application/x-texinfo" },

{ ".tgz", "application/x-compressed" },

{ ".thm", "application/vnd.eri.thm" },

{ ".tif", "image/tiff" },

{ ".tiff", "image/tiff" },

{ ".tki", "application/x-tkined" },

{ ".tkined", "application/x-tkined" },

{ ".toc", "application/toc" },

{ ".toy", "image/toy" },

{ ".tr", "application/x-troff" },

{ ".trk", "x-lml/x-gps" },

{ ".trm", "application/x-msterminal" },

{ ".tsi", "audio/tsplayer" },

{ ".tsp", "application/dsptype" },

{ ".tsv", "text/tab-separated-values" },

{ ".ttf", "application/octet-stream" },

{ ".ttz", "application/t-time" },

{ ".txt", "text/plain" },

{ ".uls", "text/iuls" },

{ ".ult", "audio/x-mod" },

{ ".ustar", "application/x-ustar" },

{ ".uu", "application/x-uuencode" },

{ ".uue", "application/x-uuencode" },

{ ".vcd", "application/x-cdlink" },

{ ".vcf", "text/x-vcard" },

{ ".vdo", "video/vdo" },

{ ".vib", "audio/vib" },

{ ".viv", "video/vivo" },

{ ".vivo", "video/vivo" },

{ ".vmd", "application/vocaltec-media-desc" },

{ ".vmf", "application/vocaltec-media-file" },

{ ".vmi", "application/x-dreamcast-vms-info" },

{ ".vms", "application/x-dreamcast-vms" },

{ ".vox", "audio/voxware" },

{ ".vqe", "audio/x-twinvq-plugin" },

{ ".vqf", "audio/x-twinvq" },

{ ".vql", "audio/x-twinvq" },

{ ".vre", "x-world/x-vream" },

{ ".vrml", "x-world/x-vrml" },

{ ".vrt", "x-world/x-vrt" },

{ ".vrw", "x-world/x-vream" },

{ ".vts", "workbook/formulaone" },

{ ".wav", "audio/x-wav" },

{ ".wax", "audio/x-ms-wax" },

{ ".wbmp", "image/vnd.wap.wbmp" },

{ ".wcm", "application/vnd.ms-works" },

{ ".wdb", "application/vnd.ms-works" },

{ ".web", "application/vnd.xara" },

{ ".wi", "image/wavelet" },

{ ".wis", "application/x-InstallShield" },

{ ".wks", "application/vnd.ms-works" },

{ ".wm", "video/x-ms-wm" },

{ ".wma", "audio/x-ms-wma" },

{ ".wmd", "application/x-ms-wmd" },

{ ".wmf", "application/x-msmetafile" },

{ ".wml", "text/vnd.wap.wml" },

{ ".wmlc", "application/vnd.wap.wmlc" },

{ ".wmls", "text/vnd.wap.wmlscript" },

{ ".wmlsc", "application/vnd.wap.wmlscriptc" },

{ ".wmlscript", "text/vnd.wap.wmlscript" },

{ ".wmv", "audio/x-ms-wmv" },

{ ".wmx", "video/x-ms-wmx" },

{ ".wmz", "application/x-ms-wmz" },

{ ".wpng", "image/x-up-wpng" },

{ ".wps", "application/vnd.ms-works" },

{ ".wpt", "x-lml/x-gps" },

{ ".wri", "application/x-mswrite" },

{ ".wrl", "x-world/x-vrml" },

{ ".wrz", "x-world/x-vrml" },

{ ".ws", "text/vnd.wap.wmlscript" },

{ ".wsc", "application/vnd.wap.wmlscriptc" },

{ ".wv", "video/wavelet" },

{ ".wvx", "video/x-ms-wvx" },

{ ".wxl", "application/x-wxl" },

{ ".x-gzip", "application/x-gzip" },

{ ".xaf", "x-world/x-vrml" },

{ ".xar", "application/vnd.xara" },

{ ".xbm", "image/x-xbitmap" },

{ ".xdm", "application/x-xdma" },

{ ".xdma", "application/x-xdma" },

{ ".xdw", "application/vnd.fujixerox.docuworks" },

{ ".xht", "application/xhtml+xml" },

{ ".xhtm", "application/xhtml+xml" },

{ ".xhtml", "application/xhtml+xml" },

{ ".xla", "application/vnd.ms-excel" },

{ ".xlc", "application/vnd.ms-excel" },

{ ".xll", "application/x-excel" },

{ ".xlm", "application/vnd.ms-excel" },

{ ".xls", "application/vnd.ms-excel" },

{ ".xlsx", "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" },

{ ".xlt", "application/vnd.ms-excel" },

{ ".xlw", "application/vnd.ms-excel" },

{ ".xm", "audio/x-mod" },

{".xml","text/plain"},

{".xml","application/xml"},

{ ".xmz", "audio/x-mod" },

{ ".xof", "x-world/x-vrml" },

{ ".xpi", "application/x-xpinstall" },

{ ".xpm", "image/x-xpixmap" },

{ ".xsit", "text/xml" },

{ ".xsl", "text/xml" },

{ ".xul", "text/xul" },

{ ".xwd", "image/x-xwindowdump" },

{ ".xyz", "chemical/x-pdb" },

{ ".yz1", "application/x-yz1" },

{ ".z", "application/x-compress" },

{ ".zac", "application/x-zaurus-zac" },

{ ".zip", "application/zip" },

{ ".json", "application/json" },

傳輸編碼

內容傳輸編碼（Content-Transfer-Encoding），這個區域使指定ASCII以外的字元編碼方式成為可能。形式如下：

Content-Transfer-Encoding: [mechanism]

其中，mechanism的值可以指定為“7bit”，“8bit”，“binary”，“quoted-printable”，“base64”。

7bit

7bit這裡指的是7位的ASCII編碼方式。

8bit

8位元ASCII碼。

binary

quoted-printable

因為歐洲的一些文字和ASCII字元集中的某些字元有部分相同。如果郵件訊息使用的是這些語言的話，於ASCII重疊的那些字元可以原樣使用，ASCII字元集中不存在的字元採用形如“=??”的方法編碼。這裡“??”需要用將字元編碼後的16進制數字來指定。採用quoted-printable編碼的訊息，長度不會變得太長，而且大部分都是ASCII中的字元，即使不通過解碼也大致可以讀懂訊息的內容。

base64

base64是一種將二進制的01序列轉化成ASCII字元的編碼方法。編碼後的文本或者二進制訊息，就可以運用SMTP等只支持ASCII字元的協定傳送了。Base64一般被認為會平均增加33%的報文長度，而且，經過編碼的訊息對於人類來說是不可讀的。

x-encodingname

這個值是預留的擴展。