# What is MX record? Definition and examples · Leadraft

URL: https://leadraft.co/glossary/mx-record
Summary: An MX record is a DNS record that names the mail servers accepting email for a domain, with a priority number for each server.

Glossary · Technical · Last updated October 31, 2026

# MX record

An MX record is a DNS record that names the mail servers accepting email for a domain, with a priority number for each server.

**Also called:** Mail exchanger record, MX.

MX (mail exchanger) records live in a domain's DNS. Each one names a mail server and a preference number; senders try the lowest number first. When anyone sends mail to `office@smithplumbing.com`, their server looks up the MX records for `smithplumbing.com` to know where to deliver it.

RFC 5321 section 5.1 covers the edge cases. If a domain has no MX records but does have an address (A or AAAA) record, the domain itself is treated as the mail server, the so-called implicit MX. If a domain publishes a "null MX" (`MX 0 .`, defined in RFC 7505), it is explicitly saying it accepts no mail.

MX lookups are the first real test in email verification. A domain with no way to receive mail can't have a valid address, so it fails fast and cheaply. The records also show who hosts the mail: records ending in `google.com` point to Google Workspace, and `mail.protection.outlook.com` points to Microsoft 365. That helps predict how a domain will behave in a mailbox check.

For local business lists, a missing MX record is often the first sign a business has closed or let its domain lapse. Verifiers that ignore the implicit-MX rule can wrongly mark working addresses invalid, so check how your tool handles it.

## Example

Looking up `smithplumbing.com` returns `10 aspmx.l.google.com` and `20 alt1.aspmx.l.google.com`. The business uses Google Workspace, and senders try the priority-10 server first.

## In Leadraft

Every email is MX-checked before the mailbox check, and pattern-guessed addresses are only suggested when the domain has a working mail server.

## Sources

1.  1.[IETF, RFC 5321: Simple Mail Transfer Protocol](https://www.rfc-editor.org/rfc/rfc5321)
2.  2.[IETF, RFC 7505: A "Null MX" No Service Resource Record](https://www.rfc-editor.org/rfc/rfc7505)

## Related terms

-   [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)
-   [Email verificationEmail verification is checking whether an address can receive mail, using syntax, MX and SMTP tests, without sending a message to it.](https://leadraft.co/glossary/email-verification)
-   [SPFSPF (Sender Policy Framework) is a DNS record that lists which servers are allowed to send email for a domain, so receivers can spot forgeries.](https://leadraft.co/glossary/spf)
-   [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)

## Further reading

-   [Email domain checker](https://leadraft.co/tools/email-domain-checker)
-   [How email verification works](https://leadraft.co/blog/how-email-verification-works)

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Last built: 2026-11-09