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Disable TNEF Encoding

Introduction

By default, Microsoft mail products such as Outlook, Office 365 and Exchange may send mail messages in a proprietary format known as TNEF that only other Microsoft products accept. This can result in other mail clients receiving emails which are malformed or contain a winmail.dat file instead of the email.
 
We recommend you disable TNEF encoding.

User Impact

Low
Disabling TNEF encoding will allow for more compatibility with other mail systems and clients.

There is no obvious impacts to the users.

Admin Portal Reference

In the Microsoft 365 Admin Portal;

  1. Go to the Exchange Admin Centre
  2. Click on mail flow in the menu on the left
  3. Double click Default to edit the policy
  4. Select the Never radio button under Use rich-text format to disable TNEF encoding
  5. Click Save

If Action is set to Notify

We report the setting is compliant if Use rich-text format for the default remote domain mail flow policy is set to Never.

We report the setting is non-compliant if Use rich-text format for the default remote domain mail flow policy is set to Always or Follow user settings.

If Action is set to Enforce

We report the setting is compliant if Use rich-text format for the default remote domain mail flow policy is set to Never.
 
We report the setting is compliant-fixed if Use rich-text format for the default remote domain mail flow policy was set to Always or Follow user settings but MSPMagic has updated the setting to Never.

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