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MX lookup

See which mail servers accept email for a domain, in the order senders will try them.

A host name works too, like mail.example.com.

More options

Which DNS server to ask. The default is Cloudflare; pick "the domain's own nameserver" to skip every cache and see exactly what the zone publishes.

Set the DNSSEC OK bit: include RRSIG records and report whether the resolver validated the answer (AD flag).

Try:

Results for google.com

Checked live lookup6 ms

JSONCheck again

NOERROR

1 record found

Everything came back normally. Open any type below to copy its values.

MX · 1
Record mix
  • MX1 of 1

1 record in 1 type.

Answered in
6ms

Google Public DNS

Lowest TTL
140s

Changes reach caches within this time

DNSSEC
Not checked

Turn on DNSSEC in More options to check

MX1
NameTTLValue
google.com2.3 min10 smtp.google.com.
Structured result (JSON) · 637 B
{
  "name": "google.com",
  "type": "MX",
  "resolver": "google",
  "resolverName": "Google Public DNS",
  "rcode": "NOERROR",
  "ad": false,
  "dnssec": false,
  "ms": 6,
  "records": [
    {
      "name": "google.com",
      "type": "MX",
      "ttl": 140,
      "data": "10 smtp.google.com.",
      "fields": {
        "preference": 10,
        "exchange": "smtp.google.com"
      }
    }
  ],
  "authority": [],
  "queries": [
    {
      "type": "MX",
      "rcode": "NOERROR",
      "records": 1,
      "ms": 5,
      "ad": false
    }
  ],
  "ede": [],
  "notes": [],
  "truncated": false,
  "server": "8.8.8.8",
  "minTtl": 140
}

What MX records do

MX records say where a domain's email goes. When someone writes to [email protected], their server asks DNS for the MX (mail exchanger) records of example.com. Each record has a priority number and the hostname of a mail server. The sender tries the lowest number first and moves up if that server cannot be reached. Servers with the same number share the load.

An MX lookup answers the first question in almost every email problem: where is this domain's mail supposed to go? It also shows which provider hosts the mailboxes.

How to check where email goes

  1. Enter the domain after the @For [email protected], look up example.com. If you paste the full address, LookupOwl takes the domain part for you.
  2. Read the prioritiesLower numbers are tried first, so priority 10 comes before 20. Equal numbers are used in random order.
  3. Check each mail serverEvery mail server hostname should have an address. Use an A lookup on any that look wrong.
If the MX looks likeMail is hosted by
smtp.google.com or aspmx.l.google.comGoogle Workspace
yourdomain-com.mail.protection.outlook.comMicrosoft 365 (Exchange Online)
mx.zoho.com, mx2.zoho.comZoho Mail
mail.protonmail.ch, mailsec.protonmail.chProton Mail
in1-smtp.messagingengine.comFastmail

These are typical patterns. Your provider's setup page has the final word, and providers sometimes change their recommended hostnames.

Reading the records

  • Priority (preference). A number where lower means preferred. Only the order matters, not the gaps, so 10, 20, 30 and 1, 2, 3 behave the same.
  • Mail server (exchange). A hostname, never an IP address and not a CNAME (RFC 2181 section 10.3).
  • Backup MX. A higher-numbered record meant as a fallback. Today you rarely need one, because senders keep retrying for days. A backup that filters spam less well than the main server can become a way around your protection.
  • Null MX (0 .). A single record with a dot as the host means the domain accepts no email at all (RFC 7505). Senders fail straight away instead of retrying. LookupOwl points this out when it sees one.
  • No MX records. The sender falls back to the domain's A or AAAA record, as if it were the mail server (RFC 5321 section 5.1). That is allowed, but easy to get wrong.

Common mail routing problems

  • Mail still goes to the old provider after a move. Senders cached the old MX records. Lower the TTL a day before you switch, and keep the old mailboxes open until it runs out.
  • Bounces say the domain cannot be found. The domain has no MX and no A record, or the mail server's hostname does not resolve.
  • The MX points to a CNAME or an IP address. Both are invalid. Point it to a hostname that has an A or AAAA record.
  • Two providers at once. MX records from different providers at the same priority split your mail unpredictably.
  • Mail arrives but lands in spam. MX is only half the story. Check the SPF record and the DMARC policy.
  • Subdomains. Mail for [email protected] needs MX records on mail.example.com. The root domain's MX does not apply.

How it works and the standards

LookupOwl asks DNS for type MX (code 15) and lists each record with its preference, mail server and TTL. The mail rules that use them are in RFC 5321 (SMTP, section 5.1 on finding the target host). The record itself is defined in RFC 1035, the null MX convention is RFC 7505, and the ban on pointing MX at a CNAME comes from RFC 2181.

Shell
dig +short MX example.com
nslookup -type=MX example.com

Questions people ask

What is an MX record?

An MX record is a DNS record that tells the world which servers receive email for a domain. Each one has a priority number that sets the order in which senders try the servers. Without MX records, senders fall back to the domain's address records, which is rarely what you want. Every domain that receives email should have them.

Which MX priority is used first?

The lowest number is used first. A record with priority 5 is tried before one with priority 10. If several records share the lowest number, the sender picks among them at random, which shares the load. A higher-numbered server is only used when the lower ones cannot be reached.

How do I find out who hosts a domain's email?

Look up its MX records and read the hostnames. They normally name the provider, such as Google, Microsoft or Zoho. A company can also run its own mail server, or put a filtering service in front of the real provider, in which case the MX shows the filter. The table above lists common patterns.

Can an MX record point to an IP address?

No. An MX record must name a host, and that host needs an A or AAAA record. Using an IP address or a CNAME breaks the standards, and many servers will refuse to deliver mail to it. If you only have an IP address, create a hostname for it first and point the MX at that.

What is a null MX record?

A null MX is a single MX record with priority 0 and a dot as the target. It tells senders that the domain never receives email, so they reject the message straight away instead of retrying for days. Use it for domains that only send mail or are parked.

How long do MX changes take?

The new records are live at once on the authoritative servers. Senders that cached the old ones keep using them until the old TTL runs out, so plan around that number. Lower the TTL a day before the switch, and keep the old mailboxes open until the change has fully settled.

Do I need a backup MX?

Usually not. Sending servers queue mail and retry for several days when the main server is down, so nothing is lost. A backup that is less protected than the primary can let spam through, because senders may try it first. Skip it unless your mail provider tells you to add one.

Use it from AI, the API or the command line

Every LookupOwl tool is also a free API and an MCP tool, with no key and no account. This one is dns_lookup. Please be kind to the rate limits.

curl
curl "https://lookupowl.com/api/v1/tools/dns-lookup?q=google.com&resolver=google"
MCP
claude mcp add --transport http lookupowl https://lookupowl.com/mcp

Description for AI agents · OpenAPI · llms.txt