At work, I use the Thunderbird e-mail client (I cannot recommend it above Microsoft’s Outlook, although you can’t beat the price), and every so often get an e-mail which is supposed to have an Excel attachment. However, there’s only a winmail.dat file, which is full of gibberish.
The problem is with (at least) some versions of Outlook, which don’t necessarily get along with other e-mail clients. It’s not politically expedient for me to say “Y0r email client sux, n00bler”, so I used the following solution:
1. Open up the winmail.dat attachment in a text editor.
2. Search for the string “ÐÏ” (without quotes) in the file, and delete everything before it.
3. Save the file as an Excel file.
Presto; you now have a spreadsheet.
However, upon doing some actual research on the problem, there’s a program called Winmail.dat Reader which will do the conversion for you. Mac users can use TNEF. Please note I haven’t tried these out.
If you are the one using Outlook and don’t want to bother your friends with the mysterious winmail.dat attachment, send a plain text e-mail if you’re sending an attachment (configurable for each recipient in address book, or use the Format menu if it’s a one-time thing).