MX Record Lookup

About MX record lookup

MX Record Lookup lists the mail exchangers for a domain in priority order, resolves each mail host to its IPv4 and IPv6 addresses and then checks for the mistakes that quietly break email delivery. It is aimed at anyone setting up or debugging inbound mail for a domain.

How to use it

1. Enter a bare domain such as example.com in the Domain box. Do not include http://, a path or a port.
2. Press Look up MX. Our server queries the MX set and then looks up each host's addresses.
3. Read the summary banner, which reports the number of exchangers and turns amber or red when it finds problems.
4. Review the MX records table for Priority, Mail host, IPv4 and IPv6. A red CNAME badge marks a host that is itself an alias.
5. Open the Diagnostics list for plain-language explanations of each finding.

Two hosts sharing one priority

mail.example.com priority 10 and mail2.example.com priority 10

Warning: Duplicate priority 10. Both hosts share priority 10, which is legal and load-balances between them, but is often a typo when a primary and a backup were intended.

When to use it

• Checking that a newly added Google or Microsoft mail setup is published correctly.
• Finding out why senders report that mail to a domain bounces immediately.
• Verifying a null MX is in place on a domain that should never receive email.
• Auditing whether a domain depends on a single mail server with no backup.

Questions about MX record lookup

Why is an MX pointing at a CNAME an error?

The mail specifications require an MX target to be a name with address records, not an alias. Some senders follow the alias anyway, others refuse to deliver, so the safe fix is pointing the MX at the canonical host name.

What is a null MX?

A single MX of a dot at priority 0, defined in RFC 7505. It announces that the domain accepts no mail so senders can reject at once instead of retrying for days. The tool reports it as informational rather than an error.

Does the lowest priority number win?

Yes. Senders try the lowest number first and fall back to higher numbers if it is unreachable. The table is sorted the same way, and only the first 20 exchangers are examined.

Does this test whether a mail server accepts messages?

No, it does not open an SMTP connection. It confirms the DNS side, meaning the records exist and every host resolves, which is the most common cause of delivery failures.

Is my domain sent to a server?

Yes, our server runs the DNS queries. Each query has a 5 second timeout, and about 20 lookups per minute are allowed per visitor.

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• DNS LookupLook up DNS records for a domain
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