Question:
I sometimes receive e-mail messages with a “winmail.dat” file attached that I cannot open. Why does this happen, and what can I do to fix it?
 
Answer:
This is caused by the person sending you the email and not our mail servers.

The winmail.dat file usually appears because various mail programs handle message formats differently. Certain messages sent from the Microsoft Outlook mail program (or a Microsoft Exchange server) may arrive with a winmail.dat attachment if your own mail program is not set up to handle mail in the Microsoft Outlook Rich Text Format.

Unlike plain-text formatting, this Rich Text Format can display different text styles, fonts and colors within a message. The winmail.dat file contains the Rich Text Format information for the message, but usually will not open normally. (These attachments are sometimes called T.N.E.F. files, short for Transport Neutral Encapsulation Format, which is the technical term for the format Outlook uses.)

If the winmail.dat file needs to be opened to read the message or its intended file attachment, there are a few ways to troubleshoot. One is to ask the sender to change Outlook’s settings so that mail can be sent in the plain-text format, and then to resend the original message. Microsoft has information on how to do this at the following locations:

• http://support.microsoft.com/kb/290809
• http://support.microsoft.com/?kbid=138053

Another approach is to download a program that can translate the winmail.dat file. Several developers have created helpful programs that can open the files. The MozillaZine site has a list of shareware for Windows, Mac OS X and Linux systems, along with more information about dealing with winmail.dat files, at kb.mozillazine.org/Winmail.dat_attachments.

Users with Microsoft Word can sometimes get to the text in the winmail.dat file by opening it from within Word and scrolling down through a lot of garbled code until they reach the main content of the file.