I know that netwinsite.com has been forged into a slew of "Mobster I. Syphilitic" spams, as a bogus Received: header, but I would not block mail simply based on the domain.
Chris Pugmire chrisphome@netwin.co.nz is the contact I worked with over at Surgweb to clear up the forged Received: headers issue. He was very antispam when I talked to him, perhaps he would be interested to know if he's got some spamming customer(s).