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TNEF
Last modified: Tuesday, July 27, 2004
Pronounced tee-neff, and short for Transport Neutral Encapsulation Format, a proprietary format used by the Microsoft Exchange and Outlook e-mail clients when sending messages formatted as Rich Text Format (RTF). When Microsoft Exchange thinks that it is sending a message to another Microsoft e-mail client, it extracts all the formatting information and encodes it in a special TNEF block. It then sends the message in two parts - the text message with the formatting removed and the formatting instructions in the TNEF block. On the receiving side, a Microsoft e-mail client processes the TNEF block and re-formats the message.
Unfortunately, most non-Microsoft e-mail clients cannot decipher TNEF blocks. Consequently, when you receive a TNEF-encoded message with a non-Microsoft e-mail client, the TNEF part appears as a long sequence of hexadecimal digits, either in the message itself or as an attached file (usually named WINMAIL.DAT).
Sending Messages In Rich-Text Format Article from Microsoft's Knowledge Base that describes how to control when MS-Exchange formats messages using TNEF.
