MX Lookup
Look up a domain’s mail-server records, their priorities and the public IP addresses their hostnames resolve to. SMTP connectivity and message acceptance are not tested.
How MX records work
When someone emails [email protected], their mail server asks DNS for the MX records of example.com. Each record names a mail server and a priority number. The sender tries the lowest number first and moves to the next only if that server does not answer. Servers with the same number share the load.
So MX records decide which company receives your email. If you moved from one email provider to another, the MX records are what made the switch.
Problems this check finds
- A mail server that does not resolve: the hostname in the MX record has no IP address. Senders cannot deliver to it and fall back to the next one, or bounce the message.
- An IP address instead of a hostname: not allowed by the standard. Create a hostname for the IP and use that.
- Leftover records from an old provider: if your MX records point to two different email services, some mail ends up in an inbox you no longer check.
- No MX records at all: senders may try to deliver to the domain's own IP address instead, which usually fails.
Domains that should not receive email
If a domain never receives mail, you can publish a "null MX" record: priority 0 and a single dot as the server (0 .). It tells senders straight away that mail is not accepted, instead of letting them retry for days.
Limitations
- We check that each server resolves to an IP address. We do not connect to port 25 to test that the server accepts mail.
- The provider names come from the hostnames and are a best guess.
Questions
I changed my MX records. When will email start arriving at the new provider?
Senders keep the old MX records until their TTL runs out, often one hour. During that window, some mail may still go to the old provider, so keep the old mailbox active for a day or two. Check progress with the DNS Propagation Checker set to MX.
Do I need a backup MX?
Usually not. Sending servers retry for several days if your server is down. A backup MX that is not set up with the same spam filtering can actually attract more spam.