Why can't I receive or open attachments sent from Microsoft Outlook to my iPhone?

[iMore Question]

I can not receive or open attachments sent from microsoft outlook to my iphone

If I send an email to myself of from someone else from HTML or Rich Text, the attachments are lost or changed to a win.dat file and I can not open them. I have a custom formatted Microsoft outlook signature and logo attached in my signature line, so I need to send emails using HTML or Rich Text as default. However, if I change my format to PLAIN TEXT and send an attachment, it is received by my Iphone and can also be opened, but the signature format is plain and there is no custom corporate logo image.

How can I send emails with my custom formatted signature and logo while sending attachments and have them be "openable" on an Iphone?