How e-mail message formats affect Internet e-mails in Outlook (290809)


The information in this article applies to:

  • Microsoft Office Outlook 2003
  • Microsoft Outlook 2002
This article was previously published under Q290809
For a Microsoft Outlook 97 version of this article, see 184126.
For a Microsoft Outlook 98 version of this article, see 184123.
For a Microsoft Outlook 2000 version of this article, see 241538.

SUMMARY

Both Microsoft 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 (RTF). 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 is named Winmail.dat, and may include the following information:
  • The formatted text version of the message (for example, font information and colors).
  • OLE objects (for example, embedded pictures and embedded Microsoft Office documents).
  • Special Outlook features (for example, custom forms, voting buttons, and meeting requests).
  • Regular file attachments that were added to the original message.
In addition to the previously listed information, the path to your personal folders (.pst) file and your log on 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, they can see the path and log on name. Note that the password information is not revealed. To ensure that the path to your .pst file or your log on name is not included in the Winmail.dat attachment, use the steps in this article to send messages that does not include the Winmail.dat file.

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 are not received. Alternatively, for sending messages with regular file attachments, TNEF is not needed. If you are sending messages with file attachments to a recipient who does not use Outlook or the Exchange Client, you should manually choose to use an e-mail format that does not require TNEF (such as plain text). By not sending TNEF messages, the recipient is able to view and save the attachments as expected.

Sending and Receiving Concerns

When an e-mail client that does not understand TNEF receives a message that contains TNEF information, the following are the 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 you open it because it is in the special TNEF format.

    Note Some users have reported receiving a Win.dat attachment.
  • 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, but 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 an e-mail server to strip out TNEF information from messages as it delivers them. If a server option to remove TNEF is turned on, clients always receive a plain text version of the message. Exchange Server is an example of an e-mail server program 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 by 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 by 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.

How to Control TNEF in Messages

You can control TNEF by three methods:
  • Global - If you change your default e-mail format to plain text or Hypertext Markup Language (HTML), it helps to ensure that TNEF is not sent unless an Outlook feature needs it.
  • 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.
  • Per Message - When you compose a new message, or replying to a received message.

How to Specify E-mail Format

Global Change

Use the following steps 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 box, click Plain Text or HTML, and then click OK.
Use the following steps 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 box, click to select Microsoft Outlook Rich Text Format, and then click OK.

Per Recipient Change

In the Contacts Folder

Use the following steps to turn off TNEF:
  1. Locate the recipient's record in the Contacts folder.
  2. Double-click the recipient's e-mail address.
  3. Choose Send Plain Text only in the Internet Format box.
Use the following steps to send in TNEF:
  1. Open the recipient's record in the Contacts folder.
  2. Double-click the recipient's e-mail address.
  3. Click Send Using Outlook Rich Text Format in the Internet Format box.
In the Personal Address Book

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

Per Message Change

Use the following steps to turn off TNEF.
  1. Open a New mail message, or click Reply on a recently received message.
  2. On the Mail Format toolbar, click to select Plain Text or HTML from the dropdown menu.
Use the following steps to turn on TNEF.
  1. Open a New mail message, or click Reply on a recently received message.
  2. On the Mail Format toolbar, click to select Rich Text from the dropdown menu.

Common Scenarios

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

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

  • Problem: Recipient does not receive regular file attachments.
    Solution: Turn TNEF off (either for the recipient, or globally).

  • Problem: Recipient does not have Voting buttons in Outlook.
    Solution: Turn TNEF on for the recipient.

  • Problem: Recipient receives meeting requests as regular 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:3/30/2005
Keywords:kbemail kbhowto KB290809
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