Free tool
MX lookup
See where a domain’s email goes: its MX records in the order senders try them, the addresses of up to ten mail servers, and the provider behind them, read live from public DNS.
- IPv4 and IPv6 addresses for up to ten mail servers, in sending order
- Null MX, implicit MX, aliases and dead hosts explained
- Nothing sent to Kawaa: the lookup runs in your browser
Resolved live from your browser by a public DNS-over-HTTPS resolver (Cloudflare, with Google as fallback). Only the domain is looked up, never the part of an address before the @, and it goes to the resolver, not to Kawaa. Nothing is stored and no email is sent.
Reading the answer
What an MX lookup can tell you
Most domains answer with a short list of mail servers that all work. The rest fall into a handful of cases, and each one means something specific for mail sent to the domain. These are the cases the lookup recognizes, and how Kawaa’s verifier reads each one.
MX records, in preference order
Each MX record names a mail server and a preference number. Senders try the lowest number first and move down the list when a server does not answer; servers that share a number are picked at random, which spreads the load. Only the order matters: 10 and 20 behave exactly like 1 and 2.
No MX, but an address: implicit MX
A domain without MX records can still receive mail. RFC 5321 (section 5.1) tells senders to deliver to the domain’s own A or AAAA address instead. Kawaa’s verifier does the same over IPv4, so an address at such a domain can come back valid; its servers do not connect over IPv6 yet, so a domain whose only address is IPv6 comes back unknown. It works only if a mail server answers at that address, and many web servers run none.
Null MX: no mail, on purpose
A single MX record pointing at "." (written 0 .) is the RFC 7505 way to say a domain accepts no email. Senders bounce mail to it at once instead of retrying for days, and Kawaa’s verifier reports an address there as invalid, with the reason code no_mx, without contacting any server.
An MX that points at an alias
An MX record must name a host directly, not a CNAME alias (RFC 2181, section 10.3). Many senders follow the alias anyway, and Kawaa’s verifier does, but a strict sender can refuse. The lookup shows where the alias leads, which is the name the MX should use.
An MX that names an IP address
An MX record must name a host. One that names an IP address instead is a misconfiguration many mail servers refuse to deliver to. Kawaa’s verifier dials a public IPv4 address written this way when it is among the first five hosts it tries, and skips a private or IPv6 one; the fix is a host name with an A record, and the MX pointing at the name.
A mail server that does not resolve
An MX host with no A or AAAA record, or one that does not exist, is a dead end: senders skip it and try the next. When every host is dead, mail bounces, and Kawaa’s verifier reports an address there as invalid (no_mx). A host such as mail.example.com.example.com usually means the zone file is missing a final dot.
A mail server on a private address
An MX that resolves only to a loopback or private address (an MX of localhost, or one in 10.0.0.0/8) cannot be reached from the internet. Kawaa’s verifier never dials such an address, and a domain whose mail hosts all look like that has no mail server it can use.
A domain that does not exist
NXDOMAIN means DNS has no such name: no records, so no mail. It is usually a typo or a lapsed registration. Kawaa’s verifier reports an address there as invalid, with the reason code domain_not_found.
Who runs the mail
The provider behind the MX records
Hosted mail services name their mail servers after themselves, so the MX records usually say who runs a domain’s mail. The lookup recognizes Google Workspace or Gmail, Microsoft 365, Outlook.com, Zoho Mail, Proton Mail, Fastmail, iCloud Mail, Yahoo Mail (also AOL), Yandex Mail, GMX, WEB.DE or mail.com and Amazon WorkMail or SES.
It also recognizes the filtering gateways Mimecast, Proofpoint, Barracuda and Cisco Secure Email, and Cloudflare Email Routing, which forwards mail elsewhere. A gateway receives the mail first and passes it on to a mailbox provider that DNS does not show, so behind a gateway the lookup names the gateway only.
What this is not
A DNS read, not a mailbox check
- A DNS read, not a connection. The lookup does not contact the mail servers, so it cannot tell whether one is up or whether a particular mailbox exists. The free email checker does that for one address.
- Where this page says what Kawaa’s verifier returns, it describes what the verifier concludes from these DNS records. Other checks can settle an address first: one at a known disposable-email domain, for example, is reported as disposable.
- Bounded on purpose: the first 10 mail server names are resolved, and one lookup sends at most 24 DNS queries and stops after 15 seconds. Anything left unread is labelled as such, never guessed.
- Provider names are read from the mail servers’ host names. A domain behind a filtering gateway shows the gateway, not the mailbox provider behind it, and a provider the page does not know is shown by host name only.
After the lookup
Where to go from here
Check the domain’s authentication
The free DMARC, SPF and DKIM checker reads the records that decide whether receivers trust mail sent from the domain. A domain looked up here carries over when you follow the link from a result.
Check DMARC, SPF and DKIMCheck one address
MX records say where a domain’s mail goes, not whether a mailbox exists. The free email verifier checks one address end to end, with no account.
Verify an addressVerify a whole list
Upload a CSV to a free account and every address comes back with a status, a quality score and the reason behind most verdicts.
Sign up freeThe MX record glossary entry has the short definition.
Questions
About MX records
What is an MX record?
How do I check a domain’s MX records?
Can a domain receive email without MX records?
What does an MX record of "0 ." mean?
What do the MX priority numbers mean?
Why does the lookup show different MX records from my DNS provider’s panel?
Is the domain I look up sent to Kawaa?
Verify the addresses, not just the domain
MX records say where a domain’s mail goes. Upload a list and every address comes back with a status, a quality score and the reason behind most verdicts. A free account comes with credits to start.
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