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Email verification

Email verification is a check, before you send, that an email address exists and will take mail. A verifier finds the domain's mail server, asks it about the mailbox without sending anything, and marks the address valid, invalid, catch-all or unknown.

Updated October 2026 · 4 min read · GetSales team

How email verification works

  1. Syntax. The address has to be well formed: a local part, one @ and a domain.
  2. Domain. The verifier looks up the domain's MX record, which names the servers that take its mail. A domain that does not exist fails here.1
  3. Mailbox. It opens an SMTP session with that server, names the address with the RCPT TO command and disconnects before any message is sent. A 250 reply means the server accepted the recipient, and a 550 means the mailbox is unavailable, for example not found.1 A server can add the enhanced status code 5.1.1, defined as a mailbox that does not exist.2
  4. Risk flags. Role addresses such as sales@, disposable domains and domains that accept every address are marked apart.

SMTP has a command made for this, VRFY. RFC 5321 lets a site switch it off, and a server that does must answer 252, which neither confirms nor denies the address.1 That is why verifiers ask with RCPT TO.

What the results mean

  • Valid. The server accepted the mailbox at the time of the check.
  • Invalid. The server refused the mailbox, or the domain takes no mail. A message to it bounces.
  • Catch-all. The domain accepts every address, so the check cannot tell a real mailbox from a made-up one.
  • Unknown. The server timed out, put off its answer or would not talk to the verifier.

Why verify before you send

Mail providers watch bounces. Google's sender guidelines tell senders to lower their volume when messages start bouncing, and to unsubscribe recipients after several bounced messages.3 A check before the send keeps those addresses off the list in the first place. A result holds on the day of the check, and people change jobs, so a list that has sat for months needs a fresh one.

How to verify a list

Verify when a list comes in, and again before a send if it has aged. In GetSales, verification is a setting of the Find work email column. Pick a verifier and each address is checked before it lands. The row's own address can go first, checked at the verifier's rate. A found address costs one credit when it is delivered, its check included, and a miss costs nothing.

Sources

  1. Internet Engineering Task Force, RFC 5321: Simple Mail Transfer Protocol, sections 3.3, 3.5.3, 4.2.2, 5.1 and 7.3, October 2008. Read 28 October 2026.
  2. Internet Engineering Task Force, RFC 3463: Enhanced Mail System Status Codes, section 3.2, January 2003. Read 28 October 2026.
  3. Google, Email sender guidelines, Gmail Help, requirements in force since 1 February 2024. Read 28 October 2026.

Last updated: October 2026

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