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Watchguard Firewall Email Filtering Creates Winmail.dat attachments

If you implement the SMTP proxy and the senders outside for whatever reason use RTF for their emails and include an attachment, you don’t get the complete email.

Solution

You can have the sender restore their settings to default (HTML) or do plain text and it will work, or you can modify the proxy on your end:

  1. Start Policy Manager for your XTM device.
  2. Double-click the SMTP-Proxy used for inbound email.Or, right-click the SMTP-proxy and select Modify Policy.The New/Edit Policy dialog box appears with the Policy tab selected.
  3. Adjacent to the Proxy action drop-down list, click View/Edit Proxy.The SMTP Proxy Action Configuration dialog box appears.
  4. From the Categories tree, select Headers.
  5. In the Pattern text box, type each of these patterns and click Add to add them to the Rules list.
    • X-MS-Has-Attach:*
    • X-MS-TNEF-Correlator:*
    • X-MimeOLE:*
  6. From the If matched drop-down list, select Allow.
  7. From the Categories tree, select Content Types.
  8. In the Pattern text box, type application/ms-tnef and click Add.
  9. The pattern appears in the Rules list.
  10. From the If matched drop-down list, select Allow.
  11. From the Categories tree, select Filenames.
  12. In the Pattern text box, type winmail.dat and click Remove.The winmail.dat pattern is removed from the Rules list.
  13. From the None matched drop-down list, select Allow.
  14. Save your configuration to the device.

 

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