How to avoid EtnefUnknownMapiType error

When you’re reading through the Error log, you may find lines like this:

SYSTEM          [17D0] 10:07:16 Encountered unknown MAPI type: 72, attribute: 32768 Exception: ETnefUnknownMapiType Encountered unknown MAPI type: 72, attribute: 32768

These errors typically occur when someone sends an email from Microsoft Outlook and TNEF (Transport Neutral Encapsulation Format) is used.

You can usually notice this email when a Winmail. dat file is attached, which contains the message's formatting. This can happen when RTF (Rich Text Format) is used for email composition instead of HTML or plain text.

For local users of Microsoft Outlook with Outlook Sync, it’s recommended to disable TNEF in Outlook Sync settings - Advanced.

This setting is enabled by default.

This can’t be prevented for remote senders unless they tweak the format type on their side.