# What is email verification? · Leadraft

URL: https://leadraft.co/glossary/email-verification
Summary: Email verification is checking whether an address can receive mail, using syntax, MX and SMTP tests, without sending a message to it.

Glossary · Email & deliverability · Last updated October 31, 2026

# Email verification

Email verification is checking whether an address can receive mail, using syntax, MX and SMTP tests, without sending a message to it.

**Also called:** Email validation, Email checking, Mailbox verification.

A verifier runs a short pipeline. It checks the address's syntax, looks up the domain's MX records to find its mail servers, then opens an SMTP conversation with one of them. It names the recipient with `RCPT TO`, reads the reply code, and hangs up before the `DATA` command, so nothing is delivered. A final test asks about an address that can't exist, to detect catch-all domains.

The result is a grade. A `250` reply on a domain that rejects made-up addresses means the mailbox exists: valid. A permanent `5xx` reply such as `550 5.1.1` means no such user: invalid. A server that accepts everything is catch-all. A timeout or a temporary `4xx` reply is unknown and should be retried, never marked invalid.

For local lead generation, verification is what separates a list you can send to from a list that burns your domain. Addresses found on small business websites include typos, old staff mailboxes and closed domains, and pattern guesses are often wrong. Sending tools pause campaigns on high bounce rates; Instantly, for example, auto-pauses above 5%.

Verification has limits. It measures one server reply at one moment. It can't tell whether a person reads the inbox, whether mail will land in spam, or anything certain about catch-all domains, and some large providers don't answer checks reliably. Re-verify before a send if the last check is more than about a month old.

## Example

A list of 500 dentist emails is verified the day before a campaign: 360 come back valid, 90 catch-all, 30 invalid and 20 unknown. The 360 go out first, the 90 later in a separate batch, the 30 are dropped, and the 20 are re-checked in a few days.

## In Leadraft

Every email found is checked against the live mail server and graded **Verified**, **Accept-all** or **Invalid**. Invalid emails are never exported, and a check that fails is never graded invalid: it's retried later.

## Sources

1.  1.[IETF, RFC 5321: Simple Mail Transfer Protocol](https://www.rfc-editor.org/rfc/rfc5321)
2.  2.[IETF, RFC 3463: Enhanced Mail System Status Codes](https://www.rfc-editor.org/rfc/rfc3463)
3.  3.[Instantly, High bounce auto-pause feature](https://help.instantly.ai/en/articles/9823139-high-bounce-auto-pause-feature)
4.  4.[Leadraft, Verification methodology](https://leadraft.co/methodology/verification)

## Related terms

-   [Catch-all emailA catch-all email is an address on a domain whose mail server accepts mail for any address, so a verifier can't confirm the mailbox really exists.](https://leadraft.co/glossary/catch-all-email)
-   [SMTPSMTP (Simple Mail Transfer Protocol) is the standard, defined in RFC 5321, that mail servers use to send and relay email to each other.](https://leadraft.co/glossary/smtp)
-   [MX recordAn MX record is a DNS record that names the mail servers accepting email for a domain, with a priority number for each server.](https://leadraft.co/glossary/mx-record)
-   [Bounce rateBounce rate is the percentage of sent emails that were returned as undeliverable; for cold email, under 2% is a sensible target.](https://leadraft.co/glossary/bounce-rate)
-   [Data decayData decay is the steady loss of accuracy in a lead list as people change jobs, businesses close or move, and email addresses stop working.](https://leadraft.co/glossary/data-decay)

## Further reading

-   [How email verification works](https://leadraft.co/blog/how-email-verification-works)
-   [Verification methodology](https://leadraft.co/methodology/verification)
-   [Emails in Leadraft](https://leadraft.co/product/emails)

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Last built: 2026-11-09