Two terms get used as if they mean the same thing: MX lookup and SMTP verification. They do not. Picking the wrong one, or expecting one to do the job of the other, is how teams end up rejecting good customers or trusting bad addresses. The distinction is narrower than the marketing copy suggests. What an MX lookup proves An MX (mail exchanger) record tells the world which mail servers accept mail for a domain. Looking it up is a DNS query. If a domain has MX records, mail can, i...