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MX record lookup

Reads the mail exchangers for a domain, resolves each one, and tells you whether mail can actually be delivered, not just what is published.

Judged against RFC 5321, with null MX from RFC 7505

Free, instant, no signup. This test reads your live DNS the way a receiving server does.

Symptoms

MX problems are the loud kind: mail to you bounces, or stops arriving from one particular sender while everything else looks normal. The quieter version is a backup server nobody has tested in three years, which turns out not to resolve on the day the primary goes down.

Diagnosis

An MX record tells the world where to deliver mail for your domain, and in what order to try. A sender takes the lowest priority number first, resolves that hostname to an address, and connects. Every step in that chain can be published correctly and still fail.

  • The target must be a hostname, not an IP address, and not an alias. The standard forbids pointing an MX at a CNAME.
  • The target must resolve. A host with no A or AAAA record silently drops you to the next priority, or to nothing.
  • Priority is preference, not importance. Lower is tried first; equal numbers mean the sender chooses.

Cure

  1. No MX at all. If the domain should receive mail, add the records your provider documents. If it should not, publish a null MX so senders fail fast and spammers stop trying.
  2. A target that does not resolve. Add the address record, or remove the MX entry if the server is retired.
  3. A single machine. Add a second exchanger at a higher priority number. Most providers include one.

Questions people actually ask

What is a null MX record?

A single MX with priority 0 and a target of "." It states that the domain accepts no mail at all, so senders fail immediately instead of retrying for days. For a send-only or parked domain it is the correct configuration, not a fault.

Can an MX record point at an IP address?

No. An MX must name a host, and that host needs its own A or AAAA record. Strict senders reject an MX containing an IP outright.

Should my MX hosts have equal priorities?

Only if you want senders to choose between them at random, which is a valid way to share load. If you meant one to be a backup, give it a higher number, 10 and 20 rather than 10 and 10.

Do I need more than one MX record?

It depends what is behind it. One hostname resolving to several addresses is how the large providers do it and is perfectly resilient. One hostname resolving to one machine means a maintenance window turns into returned mail.

Related tests

Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.