how to check email mailbox exists
How to check email mailbox exists
Use protocol-level verification to see whether a mailbox seems to exist before you send email.
Mailbox checks are stronger than syntax checks but weaker than human confirmation.
They are especially useful for signup gating and list hygiene.
They should be handled carefully to avoid rate limiting.
220 mail.example.com ESMTP
EHLO emailverify.se
MAIL FROM:<[email protected]>
RCPT TO:<[email protected]>
QUITWhat is the best signal?
A combination of DNS, SMTP, and provider behavior is stronger than any one test.
Can this fail silently?
Yes, which is why you should log timing and result codes on the server.
What SMTP probing actually proves
SMTP probing is a protocol conversation with the recipient domain. It can indicate whether a mailbox appears to accept mail, but it also reflects server policy, temporary throttling, anti-abuse behavior, and catch-all handling.
How to use it safely
Keep probing on the server, add timeouts, respect provider limits, and avoid repeated retries against the same domain. In production, you should store only the resulting status and score, not the full transcript.
FAQ
How do I use this page?
Use it as a quickstart reference and link it from your docs, onboarding flow, or marketing page.
What should I do next?
Create an account, try the demo, and move the integration into your backend with a real API key.
Can SMTP confirm the owner is real?
No. It only suggests that the mailbox path looks reachable at the time of the check.
Why not send a message instead?
Because many products need a quiet validation path before onboarding or import completes.