There's a couple of those APIs, maybe with their parent company Twilio and sister company sendgrid they have an edge on MX block lists. With privacy in Europe

There's a couple of those APIs, maybe with their parent company Twilio and sister company sendgrid they have an edge on MX block lists. With privacy in Europe (GDPR) I don't think I could use any of them as sending the email address of a user who hasn't agreed to the privacy policy is non-essential and needs opt-in. IP address, domain maybe, but will email address to a copmany (I assume) in the United States would not be covered.