As an Exchange Online Administrator, a setting you may want to pay attention to is the use of Rich Text format in Remote Domains. When this setting is set to Always or Follow User Settings, it usually means that emails sent through the server are using Microsoft’s proprietary TNEF format. Depending on the recipient’s email server and client, this could cause things like getting an attachment of winmail.dat or seeing CID links (like [CID:image address]) instead of inline images within the body of an email. There are a few places this setting could be implemented ranging from the sender’s client, the saved contact, or the outgoing Exchange server.
How To Disable Exchange Online TNEF Globally
- Go to your Exchange Online Admin Portal
- Go to Mail Flow
- Go to Remote Domains
- Open your Default Remote Domain or create a new one
- Under Use Rich-Text Format, set it to Never
- Click Save
How To Disable Rich Text Format Per User or Contact
Using Exchange Powershell, you can change the setting per User or Contact by using these commands:
Set-MailContact -Identity email@example.com -UseMapiRichTextFormat Never
Set-MailUser -Identity firstname.lastname@example.org -UseMapiRichTextFormat Never
If you set it globally above, then you don’t need to set it per contact.