You should need the user to opt in (although if they opted in to third-party marketing from Dun & Bradstreet then presumably that is legitimate too), and then s

You should need the user to opt in (although if they opted in to third-party marketing from Dun & Bradstreet then presumably that is legitimate too), and then send them the messages, that do not contain any lies, and do not send third-party marketing from your domain (unless they opted in to third-party marketing too), and then hopefully will not be black listed. Even if they are, some users will black list stuff they do not want using various methods (I set up a different email alias for each thing and delete the aliases that start receiving messages that I do not want).