Outlook: Issues with TNEF

From Provider Wiki

Microsoft Outlook uses the TNEF protocol (Transport Neutral Encapsulation Format) when sending email messages. This protocol can only be correctly understood between Outlook clients. When sending mail with an attachment to other mail client users (including Microsoft Outlook Express), the following behaviors may occur:

• 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 order to fix this issue, the recommendation is to change the default mail format to plain text:

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.

For additional options, see the Microsoft Knowledge base article on the subject, number 290809. [1]

---Bob DeSilets