Problem of sending winmail.dat in outlook

solution (for outlook):
在 [工具] 功能表上，按一下 [選項]，然後按一下 [郵件格式]。
在 [使用這個郵件格式撰寫] 中，按一下以選取 [純文字]，然後按一下 [確定]。
Select Tools->Options from the Outlook menu bar. Select the "Mail Format" tab in the dialog window.
In the first drop-down list, under the "Message Format" heading, select Plain Text ,then click the "OK" button.

reference:
http://support.microsoft.com/kb/278061
http://www.gpc.edu/~jbenson/resource/winmail.htm
http://email.about.com/od/outlooktips/qt/et121705.htm