Transport Neutral Encapsulation Format (TNEF) is a proprietary email attachment format used by Microsoft Outlook when when sending a message using either Rich Text Format or HTML Format. An attached file with TNEF encoding is most often named winmail.dat or win.dat, and has a MIME type of "application/ms-tnef".
The Winmail.dat contains the rich text body, MAPI properties information, and original attachments.
In this article, we introduce the code that extracts the message attachments, with the original file names, and the message body, including HTML, text, and RTF.