How to View or Change Blocked File Types or MIME Types in Outlook Web Access

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In Outlook Web Access, there are two levels of attachment blocking that you can configure. These levels correspond to the different risk levels posed by file types and MIME types. Outlook Web Access does not allow Level 1 files or MIME types (specified by the attributes, Level1FileTypes and Level1MIMETypes respectively) to be downloaded in any format. Level 2 file and MIME types are less severe; users are not allowed to open them in Internet Explorer, but they can right-click the file, save it to disk, and then open it.

Important

When a user uses Internet Explorer to open a file, either saving it to disk, or selecting Open from the right-click menu in Internet Explorer, anti-virus software that is installed on Exchange Server does not scan the file for viruses. Therefore, it is critical that anti-virus software is running on the user's desktop where the file is opened.

If you want to view or change blocked file types or MIME types in Outlook Web Access, perform the following procedure.

Before You Begin

This topic discusses editing the registry.

Warning

Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

Procedure

To view or change blocked file types or MIME types in Outlook Web Access

  1. Start Registry Editor (regedit).

  2. Navigate to the following registry key:

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWeb\OWA

  3. The Level1FileTypes value shows blocked attachments; the Level1MIMETypes show blocked MIME types.

For More Information

For a list of the files that are blocked by default in Outlook Web Access, see the Microsoft Knowledge Base article, "Outlook Web Access - Configure Attachment Blocking."