I never signed up for Upwork. My account was purchased from Elance and destroyed by Upwork. I was one of the top rated proviers on Elance and after the buyout I was left with a 60% completion rate and was thus unable to bid on anything on Upwork.
Since the staff at Upwork care nothing about me or my situation I have simply asked to stop receiving notifications from this horrible company and yet they keep coming.
Are you able to log into your Upwork account?
If so, then you should be able to both change notification settings AND change your email address to an address which does not result in messages reaching you.