The Problem
Outlook is a rather powerful email client program with a number of features that look very attractive. Most notably, Outlook allows users to send email in a variety of formats:
as plain vanilla text with no formatting
in Rich Text Format, which allows for a limited amount of formatting, such as boldface/italic/underlined text or different fonts
formatted with the HTML formatting language so that it appears (sort of) like a web page
formatted as a Microsoft Word document.
It's these formatting options that cause the problems.
When an Outlook user composes and sends a message using either Rich Text Format or HTML Format, Outlook automagically 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 Outlook will use on the receiving end to display this email message correctly. Unfortunately, Outlook is the ONLY email client program that can use this information! Netscape Messenger, Eudora, Lotus Notes and other email client programs don't understand this information.
The Solutions
If you are receiving these winmail.dat files
One solution to the problem is to visit
and download the WMDecode program found there (look about halfway down the page). This will at least allow you to decode the winmail.dat files and extract any useful attachments from them.
Other than this, there's not much you can do on your end to fix the problem, since it's not your email program generating the problem. If you just don't want to deal with the problem, the other approach is to 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, not in Rich Text Format or HTML. If they don't know how to do this, you can, of course, refer them to this document!
You may 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 "Mail Format" tab in the dialog window.
3. In the first drop-down list, under the "Message Format" heading, select Plain Text
4. Click the "OK" button.