📮 Verifying an Email Address

When you want to know if an email address entered in a signup form can actually receive mail, here's exactly how far you can verify that, and where it becomes impossible.

What a format check confirms

Whether the basic [email protected] syntax is correct, and whether the domain part contains any disallowed characters, can be checked instantly.

What an MX record check confirms

Checking whether the domain has a mail server configured (an MX record) confirms, at minimum, that "this domain is capable of receiving mail." If there's no MX record, mail to that domain won't be delivered at all.

What you can't confirm — whether the mailbox exists

Whether a specific account (the "abc" in [email protected]) actually exists can't be safely checked from a browser or an ordinary server. Connecting directly to the SMTP server to probe (an "SMTP ping") exists as a technique, but most mail servers block it or return inaccurate responses to prevent spam.

A practical approach

For signup forms, filter with a format check plus an MX lookup first, then verify real deliverability by sending a confirmation email and checking that it gets clicked — that's the standard approach.

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