Problems forming attachments: The Winmail.dat dilemma

This document adapted (with permission) from a Web page maintained by Dr. Julia Benson-Slaughter.

Email users sometimes call the help desk for assistance opening email messages with a strange file attached, called winmail.dat. When they attempt to open this file, either it can't be opened at all, or it contains "garbage" data. This problem typically happens when the sender uses Microsoft Outlook 97/2002/2003. These programs do not always follow established rules for transmitting attachments, and as a result, an attachment is transmitted in this not-very-useful .dat format.

Why does it happen?

The situation causing this is that people are using several different email client programs to receive, read, and send email. The most commonly used email client programs at Lehigh are Netscape, Mozilla, or IMP. Microsoft Outlook is used elsewhere. Unfortunately, Outlook does not "play nicely" with the other email programs -- and as a result, attachments are garbled in translation. This causes problems, not for the sender of the email, but the recipient, particularly when actual files are attached to messages.

When an Outlook user composes and sends a message using either Rich Text Format or HTML Format, Outlook generates a file, winmail.dat, and attaches it to the end of the message. Winmail.dat contains formatting information, in a human-unreadable form, that can be received and interpreted by other Outlook users, but it not universally readable by other email clients. Those of us on the receiving end with other mail clients, such as Mozilla Thunderbird, IMP, or Eudora, won't be able to use/view the attachments.

What can you do?

Fortunately someone has invested the time into a fix for this issue.

1. Save the winmail.dat file to the desktop or some location you can find on your computer.
2. Go to http://www.biblet.com.
3. Click on the link "Download WMDecode.zip" (look about halfway down the page) and follow the instructions to convert the winmail.dat file to the original format.

If you do not want to use the program above, reply to the individual who sent you the offending email and ask that they re-send the message, with the attached files, as a plain text message, omitting any formatting.

If you are sending these winmail.dat files
If someone emails you to complain that they couldn't read your attachments, or to ask what this "winmail.dat" file is that you sent them, chances are you sent this email using Microsoft Outlook or Outlook Express.

The simplest fix is to change your default sending mode in Outlook, thereby sending all email messages as plain text, by doing the following:

1. Select Tools->Options from the Outlook menu bar.
2. Select the "Sending" tab in the dialog window, and locate the Mail Sending Format section of that tab.
3. Select Plain Text
4. Click the "OK" button.
   

Note that Lehigh University encourages the use of Netscape or Mozilla mail clients, for a variety of reasons. If you have additional questions, speak with your computing consultant or the help desk about your email needs.