经常用IIS作为下载服务器的时候有时传上去的文件比如 example.mp4 文件名上传后，但是用http打开的时候确显示为 404 文件不存在。其实是IIS对文件的一种保护，不在IIS指定的MIME类型里的文件不会被操作。
常见的有 mp4 / flv / iso / 7z / apk 等扩展名的文件， iis 本身是没有指定MIME类型的，这类文件默认在IIS里是不能下载的，如确需下载，则需手动添加对应的 MIME 类型。
方法如下：
1. 打开IIS，在右侧找到 MIME类型
比如我们需要IIS支持 MP4 文件下载可以这么设置：（这里我们对IIS全局进行设置、如果只针对某一个站点可以直接设置站点的）
2. 选中指定网站→在右侧找到 MIME类型 → 双击进入已有类型页 → 点击最右侧添加
3. 在弹出的 MIME类型框上 扩展名 MP4 MIME类型为： application/octet-stream
这样IIS就可以支持 MP4下载了。
下面列出一些常用的 扩展名的 MIME类型。
如果不知道MIME类型 可以写通用的: application/octet-stream
还有一些规律如果是文本类的让IE可以直接打开的 MIME 可以为 text/扩展名
如果是音频打开的时候让windows自动播放的可以用 audio/扩展名
扩展名类型/子类型
| application/octet-stream | |
| 323 | text/h323 |
| acx | application/internet-property-stream |
| ai | application/postscript |
| aif | audio/x-aiff |
| aifc | audio/x-aiff |
| aiff | audio/x-aiff |
| asf | video/x-ms-asf |
| asr | video/x-ms-asf |
| asx | video/x-ms-asf |
| au | audio/basic |
| avi | video/x-msvideo |
| axs | application/olescript |
| bas | text/plain |
| bcpio | application/x-bcpio |
| bin | application/octet-stream |
| bmp | image/bmp |
| c | text/plain |
| cat | application/vnd.ms-pkiseccat |
| cdf | application/x-cdf |
| cer | application/x-x509-ca-cert |
| class | application/octet-stream |
| clp | application/x-msclip |
| cmx | image/x-cmx |
| cod | image/cis-cod |
| cpio | application/x-cpio |
| crd | application/x-mscardfile |
| crl | application/pkix-crl |
| crt | application/x-x509-ca-cert |
| csh | application/x-csh |
| css | text/css |
| dcr | application/x-director |
| der | application/x-x509-ca-cert |
| dir | application/x-director |
| dll | application/x-msdownload |
| dms | application/octet-stream |
| doc | application/msword |
| dot | application/msword |
| dvi | application/x-dvi |
| dxr | application/x-director |
| eps | application/postscript |
| etx | text/x-setext |
| evy | application/envoy |
| exe | application/octet-stream |
| fif | application/fractals |
| flr | x-world/x-vrml |
| gif | image/gif |
| gtar | application/x-gtar |
| gz | application/x-gzip |
| h | text/plain |
| hdf | application/x-hdf |
| hlp | application/winhlp |
| hqx | application/mac-binhex40 |
| hta | application/hta |
| htc | text/x-component |
| htm | text/html |
| html | text/html |
| htt | text/webviewhtml |
| ico | image/x-icon |
| ief | image/ief |
| iii | application/x-iphone |
| ins | application/x-internet-signup |
| isp | application/x-internet-signup |
| jfif | image/pipeg |
| jpe | image/jpeg |
| jpeg | image/jpeg |
| jpg | image/jpeg |
| js | application/x-javascript |
| latex | application/x-latex |
| lha | application/octet-stream |
| lsf | video/x-la-asf |
| lsx | video/x-la-asf |
| lzh | application/octet-stream |
| m13 | application/x-msmediaview |
| m14 | application/x-msmediaview |
| m3u | audio/x-mpegurl |
| man | application/x-troff-man |
| mdb | application/x-msaccess |
| me | application/x-troff-me |
| mht | message/rfc822 |
| mhtml | message/rfc822 |
| mid | audio/mid |
| mny | application/x-msmoney |
| mov | video/Quicktime |
| movie | video/x-sgi-movie |
| mp2 | video/mpeg |
| mp3 | audio/mpeg |
| mpa | video/mpeg |
| mpe | video/mpeg |
| mpeg | video/mpeg |
| mpg | video/mpeg |
| mpp | application/vnd.ms-project |
| mpv2 | video/mpeg |
| ms | application/x-troff-ms |
| mvb | application/x-msmediaview |
| nws | message/rfc822 |
| oda | application/oda |
| 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 |
| pbm | image/x-portable-bitmap |
| application/pdf | |
| pfx | application/x-pkcs12 |
| pgm | image/x-portable-graymap |
| pko | application/ynd.ms-pkipko |
| pma | application/x-perfmon |
| pmc | application/x-perfmon |
| pml | application/x-perfmon |
| pmr | application/x-perfmon |
| pmw | application/x-perfmon |
| pnm | image/x-portable-anymap |
| pot, | application/vnd.ms-powerpoint |
| ppm | image/x-portable-pixmap |
| pps | application/vnd.ms-powerpoint |
| ppt | application/vnd.ms-powerpoint |
| prf | application/pics-rules |
| ps | application/postscript |
| pub | application/x-mspublisher |
| qt | video/quicktime |
| ra | audio/x-pn-realaudio |
| ram | audio/x-pn-realaudio |
| ras | image/x-cmu-raster |
| rgb | image/x-rgb |
| rmi | audio/mid |
| roff | application/x-troff |
| rtf | application/rtf |
| rtx | text/richtext |
| scd | application/x-msschedule |
| sct | text/scriptlet |
| setpay | application/set-payment-initiation |
| setreg | application/set-registration-initiation |
| sh | application/x-sh |
| shar | application/x-shar |
| sit | application/x-stuffit |
| snd | audio/basic |
| spc | application/x-pkcs7-certificates |
| spl | application/futuresplash |
| src | application/x-wais-source |
| sst | application/vnd.ms-pkicertstore |
| stl | application/vnd.ms-pkistl |
| stm | text/html |
| svg | image/svg+xml |
| sv4cpio | application/x-sv4cpio |
| sv4crc | application/x-sv4crc |
| swf | application/x-shockwave-flash |
| t | application/x-troff |
| tar | application/x-tar |
| tcl | application/x-tcl |
| tex | application/x-tex |
| texi | application/x-texinfo |
| texinfo | application/x-texinfo |
| tgz | application/x-compressed |
| tif | image/tiff |
| tiff | image/tiff |
| tr | application/x-troff |
| trm | application/x-msterminal |
| tsv | text/tab-separated-values |
| txt | text/plain |
再添几个常用的
apk application/vnd.android.package-archive
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