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MIME(多用途互联网邮件扩展类型) 发布于:

MIME(Multipurpose Internet Mail Extensions)多用途互联网邮件扩展类型。是设定某种扩展名的文件用一种应用程序来打开的方式类型,当该扩展名文件被访问的时候,浏览器会自动使用指定应用程序来打开。多用于指定一些客户端自定义的文件名,以及一些媒体文件打开方式。

它是一个互联网标准,扩展了电子邮件标准,使其能够支持:

非ASCII字符文本;非文本格式附件(二进制、声音、图像等);由多部分(multiple parts)组成的消息体;包含非ASCII字符的头信息(Header information)。

这个标准被定义在RFC 2045、RFC 2046、RFC 2047、RFC 2048、RFC 2049等RFC中。 MIME改善了由RFC 822转变而来的RFC 2822,这些旧标准规定电子邮件标准并不允许在邮件消息中使用7位ASCII字符集以外的字符。正因如此,一些非英语字符消息和二进制文件,图像,声音等非文字消息原本都不能在电子邮件中传输(MIME可以)。MIME规定了用于表示各种各样的数据类型的符号化方法。 此外,在万维网中使用的HTTP协议中也使用了MIME的框架,标准被扩展为互联网媒体类型。

多用途互联网邮件扩展,它是一个互联网标准,在1992年最早应用于电子邮件系统,但后来也应用到浏览器。服务器会将它们发送的多媒体数据的类型告诉浏览器,而通知手段就是说明该多媒体数据的MIME类型,从而让浏览器知道接收到的信息哪些是MP3文件,哪些是Shockwave文件等等。服务器将MIME标志符放入传送的数据中来告诉浏览器使用哪种插件读取相关文件。

MIME能够支持非ASCII字符、二进制格式附件等多种格式的邮件消息。这个标准被定义在RFC 2045,RFC 2046,RFC 2047,RFC 2048,RFC 2049等RFC中。 由RFC 822转变而来的RFC 2822,规定电子邮件标准并不允许在邮件消息中使用7位ASCII字符集以外的字符。正因如此,一些非英语字符消息和二进制文件,图像,声音等非文字消息都不能在电子邮件中传输。MIME规定了用于表示各种各样的数据类型的符号化方法。

浏览器接收到文件后,会进入插件系统进行查找,查找出哪种插件可以识别读取接收到的文件。如果浏览器不清楚调用哪种插件系统,它可能会告诉用户缺少某插件,或者直接选择某现有插件来试图读取接收到的文件,或者可能会导致系统的崩溃。传输的信息中缺少MIME标识可能导致的情况很难估计,因为某些计算机系统可能不会出现什么故障,但某些计算机可能就会因此而崩溃。

检查一个服务器是否正确设置了MIME类型的步骤是:

在Netscape浏览器中打开服务器网页。

进入"Tools"菜单,选择"Page Info"。

在弹出的窗口中点击上层框架中的"EMBED"。

在下层框架中查看MIME的类型是否为"application/x-director"或"application/x-shockwave-flash",如果是上述信息的话表明服务器已经正确设置了MIME类型;而如果MIME类型列出的是文本内容、八位一组的数据或是其它形式均表明服务器的MIME类型没有设置正确。

如果服务器没有正确标明其发送的数据的类型,服务器管理员应该正确添加相关信息,具体操作方法非常简单快捷。

Microsoft公司应用于Windows系统下的浏览器使用ActiveX控件,而不是Netscape插件,这种浏览器不必象其它浏览器那样依靠MIME的编码。"OBJECT"标签的"CLSID"属性准确地标明了应调用哪种程序来读取接收到的文件,因此浏览器不必象"EMBED"标签那样选择一种读取程序。正因为如此,你往往会在使用带插件的浏览器时遇到MIME问题,而使用ActiveX控件的浏览器则很少出现此类麻烦。

正由于上述工作方式的差别也解释了一种现象,不知你是否发现在使用Netscape浏览器播放WAV文件时,浏览器会调用LiveConnect插件进行播放,而其它浏览器一般都使用通用的QuickTime的播放插件等来进行播放,这是因为Netscape浏览器接收文件需要读取MIME标识符,以便决定调用哪种程序来读取接收的文件,而服务器设置在Netscape浏览器中播放WAV文件应使用LiveConnect插件,因此Netscape浏览器接收到WAV格式的文件时必然就会调用LiveConnect插件,但由于其它浏览器不使用这种方式,因此它们都使用系统默认的播放WAV格式文件的播放器。当然Flash电影文件并不存在这种问题,因为只有Flash播放器才能够正确读取这种格式的文件。

在把输出结果传送到浏览器上的时候,浏览器必须启动适当的应用程序来处理这个输出文档。这可以通过多种类型MIME(多功能网际邮件扩充协议)来完成。在HTTP中,MIME类型被定义在Content-Type header中。

例如,假设你要传送一个Microsoft Excel文件到客户端。那么这时的MIME类型就是“excel”。在大多数实际情况中,这个文件然后将传送给Excel来处理(假设我们设定Excel为处理特殊MIME类型的应用程序)。在ASP中,设定MIME类型的方法是通过Response对象的ContentType属性。

最早的HTTP协议中,并没有附加的数据类型信息,所有传送的数据都被客户程序解释为超文本标记语言HTML 文档,而为了支持多媒体数据类型,HTTP协议中就使用了附加在文档之前的MIME数据类型信息来标识数据类型。

MIME意为多功能Internet邮件扩展,它设计的最初目的是为了在发送电子邮件时附加多媒体数据,让邮件客户程序能根据其类型进行处理。然而当它被HTTP协议支持之后,它的意义就更为显著了。它使得HTTP传输的不仅是普通的文本,而变得丰富多彩。

每个MIME类型由两部分组成,前面是数据的大类别,例如声音audio、图象image等,后面定义具体的种类。

常见的MIME类型(通用型):

超文本标记语言文本 .html text/html

xml文档 .xml text/xml

XHTML文档 .xhtml application/xhtml+xml

普通文本 .txt text/plain

RTF文本 .rtf application/rtf

PDF文档 .pdf application/pdf

Microsoft Word文件 .word application/msword

PNG图像 .png image/png

GIF图形 .gif image/gif

JPEG图形 .jpeg,.jpg image/jpeg

au声音文件 .au audio/basic

MIDI音乐文件 mid,.midi audio/midi,audio/x-midi

RealAudio音乐文件 .ra, .ram audio/x-pn-realaudio

MPEG文件 .mpg,.mpeg video/mpeg

AVI文件 .avi video/x-msvideo

GZIP文件 .gz application/x-gzip

TAR文件 .tar application/x-tar

任意的二进制数据 application/octet-stream

用于WAP服务器的MIME类型有:

MRP文件(国内普遍的手机)

.mrp application/octet-stream

IPA文件(IPHONE)

.ipa application/iphone-package-archive

.deb application/x-debian-package-archive

APK文件(安卓系统)

.apk application/vnd.android.package-archive

CAB文件(Windows Mobile)

.cab application/vnd.cab-com-archive

XAP文件(Windows Phone 7)

.xap application/x-silverlight-app

SIS文件(symbian平台/S60V1)

.sis application/vnd.symbian.install-archive *(下有)

SISX文件(symbian平台/S60V3/V5)

.sisx application/vnd.symbian.epoc/x-sisx-app

JAR、JAD文件(JAVA平台手机通用格式)

.jar .jad下面有

Internet中有一个专门组织IANA来确认标准的MIME类型,但Internet发展的太快,很多应用程序等不及IANA来确认他们使用的MIME类型为标准类型。因此他们使用在类别中以x-开头的方法标识这个类别还没有成为标准,例如:x-gzip,x-tar等。事实上这些类型运用的很广泛,已经成为了事实标准。只要客户机和服务器共同承认这个MIME类型,即使它是不标准的类型也没有关系,客户程序就能根据MIME类型,采用具体的处理手段来处理数据。而Web服务器和浏览器(包括操作系统)中,缺省都设置了标准的和常见的MIME类型,只有对于不常见的 MIME类型,才需要同时设置服务器和客户浏览器,以进行识别。

由于MIME类型与文档的后缀相关,因此服务器使用文档的后缀来区分不同文件的MIME类型,服务器中必须定义文档后缀和MIME类型之间的对应关系。而客户程序从服务器上接收数据的时候,它只是从服务器接受数据流,并不了解文档的名字,因此服务器必须使用附加信息来告诉客户程序数据的MIME类型。服务器在发送真正的数据之前,就要先发送标志数据的MIME类型的信息,这个信息使用Content-type关键字进行定义,例如对于HTML文档,服务器将首先发送以下两行MIME标识信息,这个标识并不是真正的数据文件的一部分。

Content-type: text/html

注意,第二行为一个空行,这是必须的,使用这个空行的目的是将MIME信息与真正的数据内容分隔开。

MIME利用了一个事实就是,RFC 822在消息体的内容中做了一点限制:唯一的限制就是只能使用简单的ASCII文本。所以,MIME信息由正常的Internet文本邮件组成,文本邮件拥有一些特别的符合RFC 822的信息头和格式化过的信息体(用ASCII 的子集来表示的附件)。这些MIME头给出了一种在邮件中表示附件的特别的方法。

一个普通的文本邮件的信息包含一个头部分(To: From: Subject: 等等)和一个体部分(Hello Mr.,等等)。在一个符合MIME的信息中,也包含一个信息头并不奇怪,邮件的各个部分叫做MIME段,每段前也缀以一个特别的头。MIME邮件只是基于RFC 822邮件的一个扩展,然而它有着自己的RFC规范集。

头字段

MIME头根据在邮件包中的位置,大体上分为MIME信息头和MIME段头。(译者:MIME信息头指整个邮件的头,而MIME段头只每个MIME段的头。)

MIME信息头有:

MIME-Version:

这个头提供了所用MIME的版本号。这个值习惯上为1.0。

Content-Type:

它定义了数据的类型,以便数据能被适当的处理。有效的类型有:text,image,audio,video,applications,multipart和message。注意任何一个二进制附件都应该被叫做application/octet- stream。这个头的一些用例为:image/jpg, application/mswork,multipart/mixed,这只是很少的一部分。

Content-Transfer-Encoding:

这是所有头中最重要的一个,因为它说明了对数据所执行的编码方式,客户/MUA 将用它对附件进行解码。对于每个附件,可以使用7bit,8bit,binary ,quoted-printable,base64和custom中的一种编码方式。7bit编码是用在US ASCII字符集上的常用的一种编码方式,也就是,保持它的原样。8bit和binary编码一般不用。对人类可读的标准文本,如果传输要经过对格式有影响的网关时对其进行保护,可以使用quoted printable 。Base64是一种通用方法,在需要决定使用哪一种编码方法时,它提供了一个不用费脑子的选择;它通常用在二进制,非文本数据上。注意,任何非7bit 数据必须用一种模式编码,这样它就可以通过Internet邮件网关!

Content-ID:

如果Content-Type是message/external-body或multipart/alternative时,这个头就有用了,它超出了本文的范围。

Content-Description:

这是一个可选的头。它是任何信息段内容的自由文本描述。描述必须使用us-ascii码。

Content-Disposition:

一个试验性的头,它用于给客户程序/MUA提供提示,来决定是否在行内显示附件或作为单独的附件。

MIME段头(出现在实际的MIME附件部分的头),除了MIME-Version头,可以拥有以上任何头字段。如果一个MIME头是信息块的一部分,它将作用于整个信息体。例如,如果Content-Transfer-Encoding显示在信息(指整个信息)头中,它应用于整个信息体,但是如果它显示在一个MIME段里,它"只能"用于那个段中。

注意:其可以对自动对收到的邮件进行解密。

格式前面为后辍名,后面为对应的MIME型(例如:rar application/x-rar-compressed 表示。RAR对应的是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" },

内容传输编码(Content-Transfer-Encoding),这个区域使指定ASCII以外的字符编码方式成为可能。形式如下:

Content-Transfer-Encoding: [mechanism]

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

7bit

7bit这里指的是7位的ASCII编码方式。

8bit

8位元ASCII码。

binary

quoted-printable

因为欧洲的一些文字和ASCII字符集中的某些字符有部分相同。如果邮件消息使用的是这些语言的话,于ASCII重叠的那些字符可以原样使用,ASCII字符集中不存在的字符采用形如“=??”的方法编码。这里“??”需要用将字符编码后的16进制数字来指定。采用quoted-printable编码的消息,长度不会变得太长,而且大部分都是ASCII中的字符,即使不通过解码也大致可以读懂消息的内容。

base64

base64是一种将二进制的01序列转化成ASCII字符的编码方法。编码后的文本或者二进制消息,就可以运用SMTP等只支持ASCII字符的协议传送了。Base64一般被认为会平均增加33%的报文长度,而且,经过编码的消息对于人类来说是不可读的。

x-encodingname

这个值是预留的扩展。


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