The conversion between the format needed by the end client on the Internet is performed on the last Hub Transport server before final delivery, and when the Hub Transport role of an Exchange Server is about to deliver the message to a mailbox role server, the message is converted to MAPI format for storage. Internal communications between Exchange Servers (2000 and later) over SMTP encode the message in S/TNEF (Summary TNEF) format.
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When sending plain text or HTML format messages, some versions of Outlook (apparently including Outlook 2000 ) prefer MIME, but may still use TNEF under some circumstances (for example, if an Outlook feature requires it).
![eagetmail 45 eagetmail 45](https://lasoparunner874.weebly.com/uploads/1/2/6/4/126495376/512168688.jpg)
Selecting RTF as the format for sending an e-mail implicitly enables TNEF encoding, using it instead of the more common and widely compatible MIME standard. Within the Outlook e-mail client, TNEF encoding cannot be explicitly enabled or disabled (except via a registry setting ). Other TNEF files may contain files which have been attached to an e-mail message. Some TNEF files contain information used only by Outlook to generate a richly formatted view of the message, such as embedded (OLE) documents or Outlook-specific features such as forms, voting buttons, and meeting requests. 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 official (IANA) media type, however, is application/vnd.ms-tnef. Transport Neutral Encapsulation Format or TNEF is a proprietary email attachment format used by Microsoft Outlook and Microsoft Exchange Server.