An extension filter extracts a file attachment extension using an email's MIME headers and applies a decision based on the extension filter settings.
Go to Filtering > Attachments and select the Extension Filters tab. Extension filters that have been created at a higher level of access and applied to your domain(s) are displayed with "(inherited)" following the filter name – for example, js (inherited).
After creating or editing a filter, or number of filters, select Apply Filters to apply the filters to your mail. This button is not available for five minutes after selection.
Caution
If a filename extension has been modified, it may not be recognized by an extension filter. For example, if an executable file, photo.exe, has been renamed to photo.jpg, an .exe extension filter will not detect this change. In this situation, a File Type Filter and/or a MIME Type filter are also necessary.
Go to Filtering > Attachments and select the Extension Filters tab.
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Select Create and the Create An Extension Filter window displays.
Extension: Enter a file extension. Only alphanumeric characters are allowed for filename extensions.
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Inbound action: Select the action to take on inbound emails that match this filter:
Allow: Allow the email.
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Block: Block the email.
Important
The domain or user policy determines if the message is quarantined. Go to Policies > Domain Policy or User Policies.
Ignore: Take no action.
Scan Archives: Select if you want this filter to match files contained within compressed archive files.
Scan Double Extensions: Select to identify attachments that have been renamed to conceal their true type, as double extensions can be used to trick a user into opening malware. A mail client may hide a second extension, so filename.gif.exe appears as filename.gif.
Comments (optional): Enter optional comments about this extension filter.
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Select Create or save this extension filter or Cancel to discard changes.
Important
After creating or editing a filter, or number of filters, select Apply Filters to apply the filters to your mail. This button is not available for five minutes after selection.
