POSTDATA(1).ATT Open with ??

Client using Web Page has a FORM that is filled in and ACTION “MAILTO:email@address”

When form completed email is sent with an attached file POSTDATA(1).ATT.
But what can be used to open it with.

Tried NOTEPAD and results look like
recipient=Enquires@cavershamvehiclehire.com&subject=Internet+Enquiry&redirect=http%3A%2F%2Fcavershamvehiclehire.com%2Fthankyou.html&required=email%2Cfirstname%2Clastname&missing_fields_redirect=http%3A%2F%2Fcavershamvehiclehire.com%2Frequired.html&D1=Pick+Up+Reading&D2=Pick+Up%3A+13th&D3=June&D4=2001&D5=05

Any ideas

Alan