Description of Transport Neutral Encapsulation Format (TNEF) in Outlook 2000 (241538)


The information in this article applies to:

  • Microsoft Outlook 2000
This article was previously published under Q241538
For a Microsoft Outlook 2002 and Outlook 2003 version of this article, see 290809.

SUMMARY

Outlook and the Microsoft Exchange Client sometimes use a special method to package information for sending messages across the Internet. This method is technically referred to as Transport Neutral Encapsulation Format (TNEF).

Technical information on TNEF is available at the following MSDN Web site:

http://msdn.microsoft.com

MORE INFORMATION

The use of TNEF is commonly affected by settings in Outlook that are referred to as "Microsoft Outlook Rich Text Format." Rich Text Format and TNEF are not exactly the same, but they are closely related.

A TNEF-encoded message contains a plain text version of the message, and a binary attachment that "packages" various other parts of the original message. In most cases, the binary attachment will be named Winmail.dat, and may include:
  • The formatted text version of the message (font information, colors, and such)
  • OLE objects (embedded pictures, embedded Office documents, and such)
  • Special Outlook features (custom forms, voting buttons, meeting requests, and such)
  • Regular file attachments that were added to the original message
In addition to the information listed above, the path to your personal folders file (PST) file and your logon name are embedded in the winmail.dat file. Although this data is not explicitly exposed to the recipient, if the recipient opens the winmail.dat file for editing in a binary or text editor, he can see the path and logon name. Note that no password information is revealed. To ensure that the path to your PST file or your logon name is not included in the winmail.dat attachment, use the steps in this article to send mail that does not include winmail.dat.

Some Outlook features require TNEF encoding to be understood correctly by an Internet e-mail recipient who also uses Outlook. For example, when you send a message with voting buttons to a recipient over the Internet, if TNEF is not enabled for that recipient, the voting buttons will not be received. Alternatively, for sending messages with regular file attachments, TNEF is not needed. If you are sending e-mail with file attachments to a recipient who does not use Outlook or the Exchange Client, you should manually choose to use a mail format that does not require TNEF (such as plain text). By not sending TNEF messages, the recipient will be able to view and save the attachments as expected.

Sending and Receiving Concerns

When a message containing TNEF information is received by a mail client that does not understand TNEF, there are three common results:
  • The plain text version of the message is received and it contains an attachment named Winmail.dat. The Winmail.dat attachment does not contain any useful information when opened since it is in the special TNEF format.
  • The plain text version of the message is received and it contains an attachment with a generic name such as ATT00008.dat or ATT00005.eml. In this case the client is unable to recognize the TNEF part of the message, and is unable to recognize the Winmail.dat file name, so it creates a file name to hold the TNEF information.
  • The plain text version of the message is received and the client ignores the Winmail.dat attachment. This is the behavior found in Microsoft Outlook Express. Outlook Express does not understand TNEF, but it does know to ignore TNEF information. The result is a plain text message.
In addition to the receiving client, it is not uncommon for a mail server to strip out TNEF information from mail messages as it delivers them. If a server option to remove TNEF is turned on, clients will always receive a plain text version of the message. Microsoft Exchange Server is an example of a mail server application that has the option to remove TNEF from messages.

Message Encoding

The Internet standards for encoding messages such as Multipart Internet Mail Extensions (MIME) and UUENCODE are used independently of TNEF. TNEF can exist in a MIME-encoded message as a MIME body part of type "application/ms-tnef," or in a UUENCODED message as an attachment named Winmail.dat.

When a TNEF message is sent using MIME, an entry similar to the following is added to the message: 

   ------ =_NextPart_000_01BA6275.348C1000
   Content-Type: application/ms-tnef
   Content-Transfer-Encoding: base64
 
   eJ8+IisSAQaQCAAEAAAAAAABAAEAAQeQBgAIAAAA5AQAAAAAAADoAAENgAQAAgAAAAEAAQ
   ABBJAGAEgBAAABAAAADAAAAAMAADACAAAACwAPDgAAAAACAf8PAQAAAHQAAAAAAAAAtTvC
   [. . .]

Alternatively, if a TNEF message is sent using UUENCODE, information similar to the following is added to the bottom of the message: 


   begin 600 WINMAIL.DAT
   M>)\^(C<.`0:0" `$```````!``$``0>0!@`(````Y 0```````#H``$%@ ,`
   M#@```,L'" `$``<`)P`O``4`0 $!"8 !`"$````S,S5$,C,W,#%"0T-#13$
   [. . .]

In either case, the TNEF encoding is sent to the recipient and must be understood by the receiving client to correctly display the encapsulated information.

Controlling TNEF in Mail Messages

TNEF can be controlled in three places, and is different depending on your installation of Outlook (Internet Mail Only, or Corporate or Workgroup).
  • Global: Changing your default mail format to Plain Text or HTML will help ensure that TNEF is not sent unless an Outlook feature needs it.
  • Per Message: If the message is a Rich Text Format (RTF) message, and you are using the Internet Mail Only (IMO) installation of Outlook, you can turn on or turn off TNEF for one message at a time.
  • Per Recipient: You can specify in the recipient's e-mail address to not send TNEF, so that a recipient always receives plain text versions of the message.

To Specify Mail Format in Internet Mail Only Installation

Global Change

To turn off TNEF:
  1. On the Tools menu, click Options, and then click the Mail Format tab.
  2. In the Send in this message format list, select Plain Text or HTML, and then click OK.
To send in TNEF:
  1. On the Tools menu, click Options, and then click the Mail Format tab.
  2. In the Send in this message format list, select Microsoft Outlook Rich Text Format, and then click OK.

Per Message Change

To turn off TNEF:
  1. Open the message.
  2. On the File menu, click Properties.
  3. On the General tab, clear the Send in Microsoft Outlook Rich Text Format check box.
If your default mail format is HTML or Plain Text, you will not see the check box. Per message control of TNEF is only available for Rich Text Format messages.

To send in TNEF:
  1. Open the message.
  2. On the File menu, click Properties.
  3. On the General tab, select the Send in Microsoft Outlook Rich Text Format check box.

Per Recipient Change

To turn off TNEF:
  1. Create an Outlook contact for the recipient, if one does not already exist.
  2. Type the e-mail name of the recipient in the E-mail box of the contact.
  3. Select Send using plain text to turn off TNEF.
By selecting the check box, it ensures that TNEF will not be used for any messages to this recipient.

To send in TNEF:
  1. Create an Outlook contact for the recipient, if one does not already exist.
  2. Type the e-mail name of the recipient in the E-mail box of the contact.
  3. Clear Send using plain text, to turn on TNEF.
Leaving the check box cleared does not mean that TNEF will be used for all messages. It means that if TNEF is necessary, it will be used.

To Specify Mail Format for Corporate or Workgroup Installation

Global Change

To turn off TNEF:
  1. On the Tools menu, click Options, and then click the Mail Format tab.
  2. In the Send in this message format list, click Plain Text or HTML, and then click OK.
To send in TNEF:
  1. On the Tools menu, click Options, and then click the Mail Format tab.
  2. In the Send in this message format list, select Microsoft Outlook Rich Text Format, and then click OK.

Per Message Change

TNEF cannot be specified on a per message basis in the Corporate or Workgroup installation of Outlook.

Per Recipient Change

In the Contacts Folder

To turn off TNEF:
  1. Locate the recipient in the Personal Address Book.
  2. Double-click the recipient's e-mail address.
  3. Clear the Always send to this recipient in Microsoft Exchange Rich Text Format check box, and then click OK.
To send in TNEF:
  1. Open the recipient's record in the Contacts folder.
  2. Double-click the recipient's e-mail address.
  3. Select the Always send to this recipient in Microsoft Exchange Rich Text Format check box, and then click OK.
In the Personal Address Book

To turn off TNEF:
  1. Locate the recipient in the Personal Address Book.
  2. Double-click the recipient's e-mail address.
  3. Clear the Always send to this recipient in Microsoft Exchange Rich Text Format check box, and then click OK.
To send in TNEF:
  1. Locate the recipient in the Personal Address Book.
  2. Double-click the recipient's e-mail address.
  3. Select the Always send to this recipient in Microsoft Exchange Rich Text Format check box, and then click OK.

Common Scenarios

  • Problem: Recipient receives Winmail.dat attachment.
    Solution: Turn TNEF off (either for the recipient, or globally).

  • Problem: Recipient receives ATT00001.DAT attachment.
    Solution: Turn TNEF off (either for the recipient, or globally).

  • Problem: Recipient receives no regular file attachments.
    Solution: Turn TNEF off (either for the recipient, or globally).

  • Problem: Recipient receives no voting buttons in Outlook.
    Solution: Turn TNEF on for the recipient.

  • Problem: Recipient receives meeting requests as regular mail messages.
    Solution: Turn TNEF on for the recipient.

  • Problem: Recipient does not receive custom form information.
    Solution: Turn TNEF on for the recipient.

  • Problem: Recipient does not receive formatted message text.
    Solution: Turn TNEF on for the recipient.
Modification Type:MinorLast Reviewed:10/7/2004
Keywords:kbinfo kbhowto KB241538
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