When 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.

Published by Kevin Fream

Many people don't understand their current situation and become frustrated in business and life, so I created the Delta Method and wrote the #1 Best-Seller "Change Your Game" - as featured at Harvard and NASDAQ as well as national TV news. Streamline your technology for competitive advantage using vetted IT support and take a divergent approach to personal growth. View all posts by Kevin Fream