POP3-Proxy: Content Types

The headers for email messages include a Content Type header to show the MIME type of the email and of any attachments. The content type or MIME type tells the computer the types of media the message contains. Certain kinds of content embedded in email can be a security threat to your network. Other kinds of content can decrease the productivity of your users.

You can enable the POP3-proxy to automatically detect the content type of an email message and any attachments. If you do not enable this option, the POP3-proxy uses the value stated in the email header, which clients sometimes set incorrectly. Because hackers often try to disguise executable files as other content types, we recommend that you enable content type auto detection to make your installation more secure.

For example, a .pdf file attached to an email might have a content type stated as application/octet-stream. If you enable content type auto detection, the POP3-proxy recognizes the .pdf file and uses the actual content type, application/pdf. If the proxy does not recognize the content type after it examines the content, it uses the value stated in the email header, as it would if content type auto detection were not enabled.

You can add, delete, or modify rules. You can also set values for content filtering and the action to take for content types that do not match the criteria. For the POP3-Server proxy action, you set values for incoming content filtering. For the POP3-Client action, you set values for outgoing content filtering.

When you specify the MIME type, make sure to use the format type/subtype. For example, if you want to allow JPEG images, you add image/jpg. You can also use the asterisk (*) as a wildcard. To allow any image format, add image/* to the list.

To specify the content types for automatic detection:

  1. On the Edit page for the proxy, select the Proxy Action tab.
  2. From the Attachments drop-down list, select Content Types.
    The Content Types page appears.

Screen shot of the Content Types settings

  1. To enable the POP3 proxy to examine content and determine the content type, select the Enable content type auto detection check box.
    If you do not select this option, the POP3 proxy uses the value stated in the email header.
  2. Configure the rule action.
    For more information, see Add, Change, or Delete Rules.
  3. To change settings for another category in this proxy, see the topic for that category.
  4. Click Save.

If you modified a predefined proxy action, when you save the changes you are prompted to clone (copy) your settings to a new action.

For more information on predefined proxy actions, see About Proxy Actions.

See Also

About the POP3-Proxy

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