This file is generated by Outlook Express. It is a very rare format that most email clients do not understand and receive as winmail.dat instead of receiving the attachments. Outlook does understand them since it is the one program generating them.
Please note that chances are some of your clients or providers also receive your emails with this format and may not be able to open them correctly, so it would be wise to change your Outlook settings if possible.
In these cases one of the most popular applications is http://www.winmaildat.com/
, but there are many others around which may help in these cases.
Also, according to our investigations, Gmail may comprehend and correctly receive some of these winmail.dat files, but not absolutely all of them, so it is not just a "Feng Office issue".
In this other article you may find an application to install to ThunderBird (a very popular mail client, even more than Outlook) which may open some of these files, but not all of them since they are created by Microsoft closed standards: