Should be pretty easy to find the top 100/1000/10000 companies and look at their MX records. I’d imagine it’s a large number of Office 365, GSuite by Google an

Should be pretty easy to find the top 100/1000/10000 companies and look at their MX records. I’d imagine it’s a large number of Office 365, GSuite by Google and Barracuda/ProofPoint which may point to a SaaS thing or an internal server.