What is an MX lookup?

An MX lookup reads a domain's MX records from public DNS. The result is the list of mail servers that accept email for that domain, each with a priority number. Sending servers do the same lookup before they deliver a message.

What does MX priority mean?

The priority (also called preference) tells senders which mail server to try first. The lowest number is tried first. Servers with higher numbers are backups. When two servers share the same number, the sender picks between them, which spreads the load.

What is a null MX record?

A null MX record is a single MX record with priority 0 and an empty target, written as a dot. It is defined in RFC 7505 and lets a domain say it accepts no email at all. Senders then fail on the first attempt instead of queuing the message and retrying.

What if a domain has no MX records?

The tool shows a heading reading "No MX records for" followed by the domain, with the message "No MX records found, so this domain cannot receive email." Under RFC 5321 a sender falls back to the domain's own address record if there is one; if there is none either, the mail can't be delivered. Treat a missing MX as a strong warning sign. Check the domain for typos first, then ask the domain owner whether it is used for email.

Is the MX lookup free?

Yes. The MX lookup tool is free and you don't need an account. Type a domain or email address and click Look up MX records.

How do I look up MX records with nslookup or dig?

On Windows, open a command prompt and run nslookup -q=mx followed by the domain, for example nslookup -q=mx example.com. On Mac or Linux, run dig example.com mx in a terminal. Both list the domain's mail servers with their priority numbers.

MX Lookup: Check a Domain's MX Records

Our free MX lookup shows which mail servers accept email for a domain, in the order senders try them. Use it to check a domain's MX records before you send, or after a provider switch. No sign-up needed.

How to use the MX lookup

The MX record lookup takes one domain at a time:

Type a domain (example.com) or a full email address into the "Enter a domain or email address" field. If you enter an address, the tool uses only the part after the @, so you can check a domain straight from a contact on your list.
Click Look up MX records. The button shows "Looking up..." while the query runs.
Read the results table below the field. To check a different domain, click Look up another domain.

How to read the results

When the domain has mail servers, the result starts with the heading MX records for <domain> and a line like "2 mail servers, most preferred first. Email provider: …". The table below it has three columns:

Column	What it shows
Priority	The MX preference number. Lower numbers are tried first.
Mail server	The host name of the mail server that accepts email for the domain.
IP addresses	The IPv4 and IPv6 addresses of that mail server, "no address found" if it has none, or "not looked up".

Priority. Under RFC 5321, a sending server tries the mail server with the lowest number first and moves to higher numbers if that fails. When several servers share the same number, the sender picks among them, which spreads the load.

Email provider. This shows a provider name, or "Custom / Self-hosted" when the tool shows no provider name for the domain's mail servers. "Custom / Self-hosted" doesn't necessarily mean the company runs its own mail server; it only means the tool didn't show a provider name.

IP addresses. The lookup resolves addresses for the first 10 mail servers only. A domain with more than 10 shows "not looked up" for the rest, with the note "IP addresses are shown for the first 10 of N mail servers." If an address lookup for a server fails, you see the warning "Some IP addresses of <host> could not be resolved." In that case, run the lookup again before drawing conclusions.

Null MX: "does not accept email"

If the heading reads <domain> does not accept email, the tool shows the message: "This domain publishes a null MX record, so it does not accept email."

A null MX is defined in RFC 7505. It is a single MX record with priority 0 and an empty target, written as a dot (.). The domain owner publishes it on purpose to say the domain takes no mail. Senders learn on the first attempt that the address is undeliverable, instead of queuing the message and retrying. A null MX also stops senders from falling back to the domain's address record. Treat any address at such a domain as one you can't reach by email.

No MX records

If the heading reads No MX records for <domain>, the tool shows the message: "No MX records found, so this domain cannot receive email."

Under RFC 5321 a sender falls back to the domain's own address record (A or AAAA) if there is one, and treats that host as the mail server. If there is none either, the mail can't be delivered. Treat a missing MX as a strong warning sign, and check the common problems below.

Error messages

If the lookup can't run, you see one of these messages under the field:

"Please enter a valid domain or email address": the input has no usable domain in it.
"Invalid domain format": the domain isn't written correctly, for example it has spaces or no dot.
"Could not reach DNS servers. Please try again.": the DNS query didn't get through. Wait a moment and try again.

What an MX record is

An MX (mail exchanger) record is a public DNS record that names the mail servers that accept email for a domain. Each record pairs a mail server's host name with a preference number. A domain can list one server or several; the extra ones act as backups or share the load.

Before a sending server delivers a message to name@example.com, it looks up the MX records for example.com and connects to the servers in priority order, as RFC 5321, section 5.1 describes. If the records are missing or wrong, mail doesn't reach the domain, no matter how good the message is.

Common problems

These are the issues an MX lookup can show you:

A typo in the domain. A misspelled domain may return no MX records. Check the spelling before you treat the domain as dead.
A domain that isn't used for email. Parked domains and web-only domains may publish a null MX or no MX records at all. Addresses there won't get your mail.
A changed mail provider. If a company moved to a new provider, compare the email provider the tool shows with the one you expect. A mismatch can mean the MX records still point to the old service.
Only one mail server. A single MX record works, but there is no backup server for senders to try if that one is unavailable.

Look up MX records from the command line

If you'd rather check from a terminal, Windows has nslookup built in, and dig is available on macOS and most Linux systems (nslookup.io covers more options).

On Windows (Command Prompt or PowerShell):

nslookup -q=mx example.com

On Mac or Linux:

dig example.com mx

Replace example.com with the domain you want to check. Both commands list the domain's mail servers with their priority numbers.

When to use it, and related tools

Check a domain's mail servers:

Before you send to a new domain, such as a new client's company or a partner list, to confirm it accepts email.
When a list shows bounces from one domain, to see whether the domain publishes a null MX or has no MX records. Our guide to SMTP bounce codes explains the bounce messages you'll see.
After changing your own mail provider, to confirm the new mail servers appear and the old ones are gone.

An MX record only shows that a domain can receive mail. It doesn't tell you whether a specific mailbox exists, so a bounced list isn't fixed by an MX check alone. To check a single address, verify an email address with our free verifier, and read how to check if an email is valid for the other methods.

For the authentication side of a domain, check SPF, DKIM and DMARC with our free domain health check. When you're ready to clean a whole list, every new account gets 200 free validations with no credit card required, and credits never expire. See pricing for the rest.

MX Lookup