How to configure specific MIME types for a Web CID in IIS 7.0/8.0

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  • Updated: 20 May 2016

This article describes how to configure MIME Types for a WebCID (central installation directory) using Windows Server 2008 and IIS (Internet Information Services) 7.0 and 8.0.

If you need to configure MIME types on Windows 2003, and IIS version 6, refer to the relevant section in the knowledgebase article Sophos Anti-Virus for Windows: How to create a web CID.

Important: We recommend referring to this article at regular intervals as the list of MIME type extensions is subject to change. 

Only files with extensions registered in the IIS 7.0/8.0 MIME type list will be served. All extensions must be listed, along with an accepted Content-type. (".txt" and "text/plain" for example). You will receive an HTTP Error 403.3 - Not Found error if the file extension is not allowed.

This is best practice, as all unknown extensions will be blocked by default, and you must explicitly whitelist an extension in order to allow access. (Please see for more information).

Known to apply to the following Sophos product(s) and version(s)
Sophos Anti-Virus for Windows 2000+
Sophos Anti-Virus for Mac OS X
Sophos Anti-Virus for Linux

What To Do

How to configure MIME Types in Internet Information Services (IIS) Manager

  1. Open Internet Information Services (IIS) Manager. (To do this click Start|Administrative Tools|Internet Information Services (IIS) Manager.)
  2. Select the Sophos WebCID website you have created. Under the 'Features View' area in the IIS section, double-click on 'MIME Types'. A list of the default accepted file name extensions for MIME Types will appear.
  3. Go through the list of default file extensions comparing them to the 'Sophos required MIME Type List' specified below.
  4. For every file extension not on the default list of file name extensions:
    1. On the Actions pane, click 'Add... '
    2. For the 'File name extension:' field, enter the file extension needed. For example .bdl
    3. In the 'MIME type' field, type the Content-type application/sophos-x
    4. Click OK. Your registered MIME type will be displayed.

      Note: If the Mime type exists you will receive an error 'A MIME type for this file extension already exists'. Click OK and Cancel.

  5. Repeat this process for all of the file extensions required.

    Note: Any file extension present in the “Sophos required MIME Type List” but not in the default accepted file name extensions must be added.

  6. Close Internet Information Services when finished.

Sophos required MIME Type List

Note: This list is subject to change.

CID Name
SAVSCFXP (Version 10+) ESOSX (Version 9+) savlinux


Also see 64787 to configure bin directory, double extensions, and no extensions.

See 38238.

If updating problems occur, see 64787 for troubleshooting information.

Update testing

After configuring the necessary MIME types within IIS it is recommended that you check that a test client can successfully update from the web server. If there are problems you suspect are related to files not being delivered it is recommended you test downloading the files from the web server using a browser.  

You may need to cross reference the log files of AutoUpdate and the IIS web server logs to establish the file or files that cannot be downloaded.


You can test the download of individual files from an internet browser by enabling Directory browsing, details are available here.

If you need more information or guidance, then please contact technical support.

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