The file is a rich text (or MAPI) message that is sent from Outlook to Exchange. When Exchange sends the message to an outside server it writes the MAPI message as a MIME attachment. The unfortunate side effect of this plan is if the Outlook user has someone in their address book as a person who can receive "Rich Text" then the user will receive the TNEF file whether the user uses Outlook or not.
What's new in this version:
Support PPC and Intel Macs for OS versions 10.5/10.6.