I think I would want to open the attachments..in my case my internet security would step in pretty quick to throw out anything suspicious. If I get those emails from postmaster it is usually something I have sent, even with the correct address the cc is to send it back to you. But if you haven't sent them at all, I think there should be a way of reporting this to hotmail?
Also, download a different internet security, there are several mentioned on pc advisor.
Many people say if you change passwords and include a mixture of numbers and letters, it does prevent spammers who use strange methods of getting to you. have you tried a different browser eg orange, firefox just to foil the spammers.
Not much help but something there could help.