Transport Neutral Encapsulation Format

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Transport Neutral Encapsulation Format or TNEF is a proprietary e-mail attachment format used by Microsoft Outlook and Microsoft Exchange Server. An attached file with TNEF encoding is most usually called winmail.dat or win.dat and has a MIME type of Application/MS-TNEF.

Contents 1 Overview 2 Decoding 3 RFC Compliance 3.1 Multiplatform 3.2 Posix 3.3 Mac 3.4 MS Windows 3.5 Online 3.6 Software libraries 4 References 5 External links

[edit] Overview

Some TNEF files only contain information used 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. Other TNEF files may contain files which have been attached to an e-mail message.

Within the Outlook email client TNEF encoding cannot be explicitly enabled or disabled. Selecting RTF as the format for sending an e-mail implicitly enables TNEF encoding, using it in preference to the more common and widely compatible MIME standard. When sending plain-text or HTML format messages, Outlook uses MIME.

TNEF attachments can contain security-sensitive information such as user login name and file paths^[1], from which access controls could possibly be inferred.

[edit] Decoding

Programs to decode and extract files from TNEF-encoded attachments are available on many platforms.

[edit] RFC Compliance

Native-mode Microsoft Exchange Organizations will in some circumstances send entire messages as TNEF encoded raw binary independent of what is advertised by the receiving SMTP server. As documented in Microsoft KBA #323483, this technique is not RFC compliant because these messages have the following characteristics:

• They may include non-ASCII characters outside the 0-127 US-ASCII range.
• The lines in these messages do not have to be short enough for SMTP transport.
• They do not follow the CRLF.CRLF line termination semantics as specified in Request for Comments (RFC) 821.

[edit] Multiplatform

• LookOut — Mozilla Thunderbird extension

[edit] Posix

• yTNEF — GPL TNEF extractor from the POSIX command-line, designed specifically for reading winmail.dat
• TNEF — GPL TNEF extractor from the POSIX command-line
• KTNEF — GPL TNEF extractor for KDE
• fentun Freeware decoder

[edit] Mac

• OMiC — Shareware, plugin for Apple Mail
• TNEF's Enough — Freeware decoder for Mac OS 9/X

[edit] MS Windows

• Winmail Opener Freeware decoder
• Winmail.dat Reader Freeware easy-to-use decoder
• fentun Freeware decoder
• tnef2win Freeware decoder

[edit] Online

• tud.at service — Web service and GPL licensed PHP script for reading attachments in winmail.dat files

• 62nds — Online winmail.dat attachment extractor

• www.winmaildat.com - Another online winmail.dat extractor which allows to upload up to 5MB

[edit] Software libraries

• JTNEF — GPL Java TNEF package
• Convert::TNEF -- TNEF library written in Perl
• pytnef library — TNEF access library written in Python, licensed under LGPL

[edit] References

1. ^ How e-mail message formats affect Internet e-mails in Outlook. Microsoft (2005-03-30). Retrieved on 2006-10-13.

[edit] External links

• "How e-mail message formats affect Internet e-mails in Outlook" - How to disable TNEF in Outlook 2002 and 2003
• "Description of Transport Neutral Encapsulation Format (TNEF) in Outlook 2000" - How to disable TNEF in Outlook 2000
• "How to configure Internet e-mail message formats at the user and the domain levels in Exchange Server 2003" - Includes instructions on disabling TNEF
• "Microsoft Outlook MS-TNEF handling (aka Winmail.dat or 'Part 1.2' problem of unopenable email attachments)"