unk files?

Does anyone know what a UNK file is and how I can read them? I know its something to do with email...

The "unk" extension means that the mail contained a
MIME type unknown to your mail gateway. The sender
is most likely using Microsoft Exchange or Outlook and is
sending a document in Microsoft Rich-Text format. This
happens either because the sender assumes you are
also using Microsoft or because they just accepted the
default. The mime type will be something
like "application/ms-tnef" *.
[_{MS-TNEF - Microsoft Transport Neutral Encapsulation Format} ]

The best solution is to ask the sender to change your
address in his address book so that they will stop
sending to you as if you were using Exchange or
Outlook.

Give them this link
http://support.microsoft.com/support.../q136/2/04.asp

Or you can use this freeware tool to read that without bothering the sender.
http://www.fentun.com/

I got around to finding out both of those things, RTF and Fentun but neither of them showed anything useful or even readble.