Can't figure out why winmail.dat file occurs only in webmail

Question

I have a client who mainly uses Outlook to send emails. We have set all the settings to use HTML as outlined in other winmail.dat solutions. Her problem is a little more weird. She can send an attachment to herself and me. I get the attachment fine in Outlook and in webmail. She gets the attachment fine in Outlook but in webmail it is shown as winmail.dat. We are both using the same webmail and webmail server. Someone else in her office has the same problem. I on the other hand can send a file to myself and other and it is find for me in both outlook and webmail.

Any help would be great! I am thinking the problem has to be with the webmail server. Due to the fact that when she downloads the message from the server it is fine and only show the winmail.dat when in webmail.