It is a sad fact that MSloth users often fail to recognise that some other folk just don't use their software, and send out attachments in proprietary formats the rest of us struggle with - its like great aunt Gertie who always writes to her nieces and nephews in Chinese because "there are so many Chinese on the planet that everyone must know how to speak it a little" !!!
Those annoying application/ms-tnef MIME attachments that Microsoft mail servers helpfully use to encapsulate your already MIME-encoded attachments.
Transport Neutral Encapsulation Format or TNEF is a proprietary e-mail attachment format used by Microsoft Outlook and Microsoft Exchange Server. An attached file with TNEF encoding is most usually called winmail.dat or win.dat and has a MIME type of Application/MS-TNEF.
The answer?
cd /usr/ports/converters/tnef
make install clean
(wait for ten minutes while FreeBSD downloads the software and builds it ...)
as user
$tnef -w winmail.dat
Inside the TNEF you will probably find a harmless .pdf or a not-so-harmless but usable .doc file. So what was the point of wrapping it up?