MX record lookup
An MX lookup returns the mail servers that accept email for a domain, each with a priority number where lower is tried first. A domain with no MX record cannot receive email at all, which makes this the fastest way to rule out a large share of invalid addresses.
Free, no account. Ten lookups a minute per IP.
What the priority number means
Each MX record carries a preference value, and sending servers try the lowest first. A domain listing 1 aspmx.l.google.com and 5 alt1.aspmx.l.google.com will always attempt the first unless it is unreachable, at which point the second takes over. Equal values are load-balanced.
The numbers are relative, not absolute — 1 and 10 behave exactly like 10 and 20. Only the ordering matters, which is why comparing preference values between two different domains tells you nothing.
Reading the provider from the hostname
MX hostnames give away who runs the mail, and that is often the most useful thing on this page. Google Workspace points at aspmx.l.google.com, Microsoft 365 at a *.mail.protection.outlook.com host, Zoho at mx.zoho.com, Proton at *.protonmail.ch. A hostname on the domain's own name usually means self-hosted mail.
This matters for verification because providers differ in how they answer mailbox probes. Microsoft tenants reject unknown recipients crisply; some self-hosted servers accept everything; others greylist an unfamiliar sender on the first attempt regardless of the address.
When there is no MX record
No MX means the domain cannot receive mail, so every address at it is invalid. In practice the cause is almost always a typo in the domain rather than a domain that genuinely has no mail — gmial.com has no mail server, and the useful response is to suggest gmail.com rather than simply report a failure.
One edge case is worth knowing: under the original SMTP specification, a domain with no MX but with an A record could still receive mail at that address. Most modern mail servers no longer do this, so treat a missing MX as fatal.
Common questions
- What is an MX record?
- An MX record is a DNS entry naming a mail server that accepts email for a domain, along with a priority number where lower values are tried first. A domain needs at least one to receive email; with none, every address at that domain is undeliverable.
- How do I find a domain's mail server?
- Look up its MX records — paste the domain into the tool above and it returns the mail servers in priority order. The hostname usually identifies the provider: aspmx.l.google.com for Google Workspace, a mail.protection.outlook.com host for Microsoft 365.
- Can a domain have more than one MX record?
- Yes, and most do. Multiple records provide failover: the sending server tries the lowest priority value first and falls back to the next if it is unreachable. Records sharing the same priority value are used interchangeably to spread load.
- Does a valid MX record mean an email address is real?
- No. MX proves the domain can receive mail, nothing more. The specific mailbox may not exist. Confirming that requires an SMTP conversation with the server, which is what a mailbox check does — MX is the second of several steps, not the answer.
Check everything at once
This page covers one record. The full deliverability audit runs MX, SPF, DKIM, DMARC and blocklists together and scores the domain — or read the glossary entry for the concept behind this check.
You audited one domain. Cold outreach means thousands.
This tool checks a domain you type in. It will not tell you which addresses at that domain are real.
- Bulk mailbox verification with real SMTP checks
- The email finder — name plus company to a verified address
- Website enrichment for emails, owner names and socials
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