Why the email attachment become winmail.dat ?
Since the problem of outlook settting is from sender and the email format in Outlook is RTF format, the attachment become Winmail.dat
There are some references that related to prevent the attachment become Winmail.dat after sending out.
http://email.about.com/od/outlooktips/ss/wt121705.htm
http://support.microsoft.com/kb/278061/zh-tw
According to the Micosoft Official Website, this attachment problem is related Microsoft ‘s email system. Their system is customize the attachment format in the process of sending email. In addition, this attachment formation is not support for all email systems.
If you want to solve this problem, please use plain text format to send email.