It always starts with the list. You mention 'non opt-in' lists, which is certainly more troublesome than any domain name. Your best course of action is to get a new domain, re-confirm the lists you have (requiring the subscriber to click through in order to stay on), and only accept confirmed opt-in lists moving forward. It will decimate your mailing list in the short term, but long-term eliminate your deliverability concerns and improve ROI.