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Resolve Winmail.dat Complaints


Exchange Server LogoWhen you send an e-mail to some external recipients, do they report the inability to open messages or missing attachments replaced with Winmail.dat?

The reason is because that recipient is using an e-mail client that doesn’t support Transport Neutral Encapsulation Format (TNEF). Microsoft Outlook is one of the few e-mail clients that support TNEF-encoded messages, although some third-party utilities can help convert Winmail.dat attachments.

Even though it’s not your problem, you can’t really tell that customer or vendor that their e-mail system is faulty. The good news is that you can configure Exchange or Office 365 to prevent sending TNEF messages and Winmail.dat files:

  1. Connect to Office 365 with Powershell.
  2. Run the following command:
    Set-RemoteDomain Default -TNEFEnabled $false

These steps will prevent TNEF messages from being sent to all external e-mail domains and recipients.

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