Transport Neutral Encapsulation Format

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".

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 [cite web|title=How e-mail message formats affect Internet e-mails in Outlook|url=http://support.microsoft.com/kb/290809|publisher=Microsoft|date=2005-03-30|accessdate=2006-10-13] , from which access controls could possibly be inferred.

Decoding

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

(Tip: On Mac computers running the Mac OS X Leopard operating system (and possibly earlier operating systems, as well), if the winmail.dat file contains a PDF document, one can view its content by simply renaming it after downloading it. By changing ".dat" to ".pdf," the document's contents can be viewed without the aid of additional software. If after doing so, the contents remain unviewable, the original file contains other types of documents, and the file can be simply renamed with the original ".dat" extension.)

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 [http://support.microsoft.com/kb/323483 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.

Multiplatform

* [https://addons.mozilla.org/en-US/thunderbird/addon/4433 LookOut] — Mozilla Thunderbird extension

Posix

* [http://sourceforge.net/projects/ytnef/ yTNEF] — GPL TNEF extractor from the POSIX command-line, designed specifically for reading winmail.dat
* [http://sourceforge.net/projects/tnef/ TNEF] — GPL TNEF extractor from the POSIX command-line
* [http://sourceforge.net/projects/ktnef/ KTNEF] — GPL TNEF extractor for KDE
* [http://www.fentun.com/ fentun] Freeware decoder

Mac

* [http://www.restoroot.org/OMiC OMiC] — Shareware, plugin for Apple Mail
* [http://www.joshjacob.com/macdev/tnef/ TNEF's Enough] — Freeware decoder for Mac OS 9/X
* [http://tnefDD.sourceforge.net tnefDD] — Free GPL'd decoder with drag-and-drop functionality for Mac OS X

MS Windows

* [http://www.eolsoft.com/freeware/winmail_opener/ Winmail Opener] Freeware decoder
* [http://www.kopf.com.br/winmail Winmail.dat Reader] Freeware easy-to-use decoder
* [http://www.fentun.com/ fentun] Freeware decoder
* [http://www.petersen.de/english/tnef2win tnef2win] Freeware decoder

Online

* [http://tud.at/php/tnef/index.php tud.at service] — Web service and GPL licensed PHP script for reading attachments in winmail.dat files

* [http://www.62nds.co.nz/pg/ea0h.php 62nds] — Online winmail.dat attachment extractor

* [http://www.winmaildat.com www.winmaildat.com] - Another online winmail.dat extractor which allows to upload up to 5MB

Software libraries

* [http://www.freeutils.net/source/jtnef/ JTNEF] — GPL Java TNEF package
* [http://search.cpan.org/dist/Convert-TNEF/ Convert::TNEF] -- TNEF library written in Perl
* [http://www.python.org/pypi/pytnef pytnef library] — TNEF access library written in Python, licensed under LGPL

References

External links

* [http://support.microsoft.com/kb/290809 "How e-mail message formats affect Internet e-mails in Outlook"] - How to disable TNEF in Outlook 2002 and 2003
* [http://support.microsoft.com/kb/241538 "Description of Transport Neutral Encapsulation Format (TNEF) in Outlook 2000"] - How to disable TNEF in Outlook 2000
* [http://support.microsoft.com/kb/821750 "How to configure Internet e-mail message formats at the user and the domain levels in Exchange Server 2003"] - Includes instructions on disabling TNEF
* [http://www.dwheeler.com/essays/microsoft-outlook-tnef.html "Microsoft Outlook MS-TNEF handling (aka Winmail.dat or 'Part 1.2' problem of unopenable email attachments)"]
* [http://ple-q.com/2007/10/25/membuka-attachment-winmaildat-secara-online/ "How to open file winmail.dat by online (Indonesian Version)"]