I don't use Outlook.  At some prior point in my life, an improperly configured Outlook would send attachments encapsulated in a file called winmail.dat.  The file could only be read by other people using Outlook.  I don't remember the fix but maybe that's what's happening here?  I think the format was called TNEF and at one point I had a unix program called fenton ("no tnef" backwards) that would reverse the useless winmail.dat file back to the original attachment.

Rick