Hosted email verification APIs are convenient, but there are reasons to run your own. You might need SMTP probing, which a Cloudflare Worker cannot do because it has no raw TCP. You might have volume that makes per-call pricing awkward, or data rules that keep address checking on your side of the network. The good news is that a basic verifier needs nothing but Node and its standard library. This walkthrough builds one. It checks syntax, flags disposable and free and role addresses, and resol...