Disabling TNEF globally in Exchange Online (recommended)

eperi recommends to disable TNEF globally in Exchange Online as it may cause problems with outbound mails and "winmail.dat" attachments.

Procedure

  1. In the Microsoft 365 admin center, open the menu on the left and click Admin centers > Exchange.
    The page Exchange admin center opens in a new browser tab.
  2. From the vertical menu on the left, click mail flow.
  3. Click the Remote Domains tab from the horizontal list of tabs.
  4. Edit your Default Remote Domain or create a new one.
  5. Under Use Rich-Text Format, set it to Never.
  6. Click Save.

Results

You have successfully disabled TNEF globally in Exchange Online.