Mail.app and Windows attachments

[Eagle]

Greetings, all.

Several times recently, my father has sent email, with JPEG 
attachments, to me on my Linux box.  Every time, these emails do not 
show up with JPEG attachments, but with a "winmail.dat" file attached.  
However, if my father instead sends these mails to my .Mac address, I 
receive the attachments without problem.

Other Windows users can send JPEG attachments to my Linux account, and 
I receive them without any problems.

My father doesn't know much about his Outlook Express, and I know 
absolutely nothing about it.  Anybody have any ideas of what we should 
look at so that I can receive attachments from him to my other address?

Eagle