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 are generally generated when someone sends mail from Microsoft Outlook, and TNEF (Transport Neutral Encapsulation Format) is used.
You can usually notice this mail when there’s a winmail.dat file attached, which contains the formatting of the message. This can happen when RTF (Rich Text File) is used for mail composing instead of HTML or plain text.
For local users using Microsoft Outlook with Outlook Sync, it’s recommended to have TNEF disabled 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.