MX lookup
See where a domain asks other servers to deliver its mail, lowest preference first.
An MX record tells other mail servers where to deliver mail for a domain. Each record has a preference, which is a number, and a host name. Delivery tries the lowest number first. If that host does not answer, the sender tries the next one. The host is a name, not an address. The sender looks up that name's A or AAAA records before it connects. MX is not SPF. SPF says who may send. MX says who may receive.
This page asks the public DNS resolver for the MX records of the domain you type. It does not connect to those hosts, open port 25, or send a message. A domain with no MX records has nowhere for other sites to deliver mail, unless they fall back to the domain's own address, which many will not. A null MX is the special case of preference 0 and a host of a single dot. That is a deliberate statement that the domain does not accept mail.
How to read the list
Records are shown with the lowest preference first. Two hosts with the same number are peers. Senders may pick either. A host that appears twice does not become two servers. If the only record is a null MX, the domain is refusing mail on purpose, which is healthier than publishing nothing and letting senders guess.
The names in this list are also the names an MTA-STS policy should cover, and the names an SPF mx mechanism authorizes to send. If you add a new mail host, update the MX set, the SPF record, and the MTA-STS policy file together. A host that is in MX but missing from the policy will fail MTA-STS once that policy is enforcing.
Common mistakes
- Pointing MX at an IP address. The host must be a name. Put the address on that name.
- Using a CNAME as the MX host. The MX target should be an address record, not an alias.
- Publishing a backup with a worse preference and never testing it. A backup that cannot accept mail becomes a black hole when the primary fails.
- Forgetting the trailing name on a subdomain. Mail for news.example.com uses the MX records of news.example.com, not automatically those of example.com.
After you read the list, check SPF if you care who is allowed to send, and MTA-STS if you want receivers to require TLS to these hosts. This lookup only answers where mail is supposed to go.
FAQ
Does a missing MX mean mail will bounce?
Often, yes. Some senders fall back to the domain's address records. Many treat a missing MX as a reason not to deliver. Publish MX, or a null MX if the domain should not receive mail.
What does the number mean?
It is a preference. Lower is tried first. The number is not a priority weight and it is not a port.
Do you connect to the mail server?
No. The check is a DNS query. It does not open SMTP.
Why is the same host listed twice?
The zone contains duplicate MX records. Delete the extra one. It does not add capacity.
Is the domain stored?
No. It is used for the DNS query and is not written to a log or a database.