winmail.dat attachments are caused by a Microsoft Outlook client sending a
message in Rich Text format to a non-Microsoft Outlook (e.g. Outlook
Express, Pine, The Bat!, Eudora, .etc) mail client. Said MS Outlook user
should stick to formatting e-mail messages in Plain Text or HTML.
Not sure how to translate #2, do you want to add additional extensions to
what Microsoft Outlook already blocks access to by default or something
completely different?
/neo
PS - Not sure why Outlook Express calls HTML formatted e-mail Rich Text, but
this isn't the same as Microsoft Outlook's Rich Text.