Email verification

Four checks, in order of how much they prove

1. Syntax. Does the string look like an address? Proves almost nothing. not.a.real.person@gmail.com passes.
2. Domain. Does the domain exist and have an MX record? Rules out typos and parked domains, nothing more.
3. Mailbox. Ask the domain's mail server whether this specific mailbox exists. This is the check that matters. See SMTP verification.
4. Risk flags. Is it a role address, a disposable one, or on a catch-all domain?

Many products stop at check two and still print "verified". Ask a vendor which of the four it runs.

The honest result set

A useful verifier returns more than valid and invalid:

• Verified — the server confirmed the mailbox.
• Catch-all — the server accepts everything; the address is unconfirmed.
• Unknown — the server would not answer (greylisting, timeouts, blocking).
• Invalid — the server said the mailbox does not exist.

Collapsing these into two buckets pushes the uncertainty onto you, usually as bounces.

When to verify

Before the first send, and again before reusing any list that has aged. Data decay means a list that was clean in spring is not clean in autumn.

What verification cannot tell you

A confirmed mailbox is a statement about the server, at the moment of the check. It does not say the person still works there and reads the inbox, that your message will reach the inbox and not the spam folder, or that the address is not a spam trap. Those depend on data decay, your sender reputation, and how the list was built. Verification removes the avoidable bounces. It is not a guarantee of results.

Try it on one address with the email verifier, or read how to verify a work email before you send.