[jabart]

You can also look up common cnames or historical DNS records which would always point back to the vendor. For instance, do they use sendgrid, look for a bounce. record that points to sendgrid's servers. Do they use Facebook, well if they have a Facebook page that is verified yes. I would assume that Docusign and Attlasian also list Stripe as one of their customers on their website as well. Public TXT records are not that big of a deal.