Extracting files from Winmail.dat

I received email with an attachment named "winmail.dat". What is this and how can I read it?

This is a file created by the Microsoft Outlook mail client when the user has selected RTF as the mail format. It should only ever be used in mail exchanged between users of this mail client. Unfortunately, not everyone is aware of this and files of this type are sometimes sent to user of other mail clients. The Unix tnef utility (/usr/local/bin/tnef) can decode the winmail.dat (99.99% of the time) and extract "attachments". The procedure would be:

1. Make a new directory somewhere and save the winmail.dat file into it.
2. Change directories to the dir with the winmail.dat and run /usr/local/bin/tnef -v -f
3. Any *.doc/*.xls or power point files will be extracted into the current dir. Tnef will not overwrite existing files so that's why a new, clean dir is a good idea.
4. Use the CDE file manager to go to the extraction dir and double click on the extracted file to make the helper program start and display the extracted file(s).

Alternatively you can run either PCFileViewer (/usr/local/bin/sdtpcv) or qvpunix (/usr/local/bin/qvpunix) directly on the extracted file(s).

It's also handy to inform whomever sends you a winmail.dat that almost nobody on the internet can read their attachments (even OutLook users frequently disable opening attachments because of virus fears).