Mail7

Mail7 checks whether an email address can actually receive mail. It resolves the domain, looks up the MX records and talks to the receiving server, then reports one of three answers: valid, not valid, or unknown.

The third answer is the point. Many verification services hide behind a confidence score and quietly count catch-all domains as deliverable, which inflates the pass rate and leaves the bounces for you. Mail7 says outright when a server refuses to confirm an address.

Single addresses can be checked without an account. Bulk lists and the API are for people cleaning a mailing list before a send, where a few percent of bad addresses is the difference between the inbox and the spam folder.