Checking whether an email address is valid means confirming it has correct syntax, a working domain, and an active mailbox. This guide walks through each layer of validation.
How to Check Email Validity
1. Validate the format
A valid email must contain exactly one @, a local part of 1–64 characters, and a domain with at least one dot. Reject addresses with spaces, consecutive dots, or unsupported characters.
2. Check the domain exists
Query the domain's MX or A record in DNS. A domain with no MX record cannot receive email. Domains that do not resolve at all (NXDOMAIN) are definitively invalid.
3. Test the mailbox via SMTP
Initiate an SMTP session with the receiving mail server and issue a RCPT TO command. A 250 response confirms the mailbox exists; a 550 or 5xx error means it does not.
4. Check for disposable email providers
Services like Mailinator and Guerrilla Mail generate temporary addresses. These pass syntax and SMTP checks but have no long-term engagement value. Compare the domain against known disposable provider lists.
Tools
- BillionVerify Free Email Checker — Check any single email address for free.
- BillionVerify Email Verifier — Full verification with domain, SMTP, and deliverability status.