MX lookup
Find mail exchange servers for a domain, check their priorities, and resolve their IP addresses.
How to read your MX records
MX records decide where email for a domain is delivered. They are also the quickest way to find out who actually hosts a company's mail, because the hostnames give the provider away.
- Priority is a preference, and lower wins. A sending server tries the lowest number first and moves to the next only if that one is unreachable. Priority 10 is tried before priority 20. The numbers themselves are arbitrary, only their order matters.
- The hostname identifies the provider. Names ending in
google.commean Google Workspace,outlook.commeans Microsoft 365, and a hostname on the domain itself usually means self hosted or hosted by the web host. - Every MX must resolve to an address. An MX pointing at a name with no A record is a dead route, and mail will queue and then bounce.
- No MX records means the domain accepts no mail. Some senders will fall back to the A record, but you should never rely on that.
What usually goes wrong
- Old provider still listed after a migration. The most common mail fault there is. Mail keeps flowing to the previous host, so it does not bounce and nobody notices until someone asks about a message that never arrived.
- Two providers at the same priority. Mail is split between them unpredictably. Half your messages land in a mailbox nobody reads.
- An MX pointing at a CNAME. The spec requires MX to point at a name with an address record. Some servers tolerate it, many do not, and the failures are intermittent.
- MX set on www instead of the bare domain. Mail is addressed to
user@example.com, so the records must be onexample.com. - MX correct, mail still filtered. MX controls inbound routing only. If messages arrive but land in spam, the problem is authentication or reputation, not these records.
Common questions
How do I find out who hosts a domain's email?
Look up its MX records. The hostnames name the provider directly: Google Workspace, Microsoft 365 and the major hosting companies all use recognisable mail hostnames. This works for any domain without needing access to it, because MX records are public.
What does MX priority mean?
It is the order servers are tried, and the lowest number goes first. Higher numbers are fallbacks used only when the preferred server does not answer. It is not a weighting or a load balance, so two records at the same priority split mail rather than preferring one.
How long does an MX change take?
Up to the TTL on the record, so mail can keep arriving at the old provider for that long after the change. Lower the TTL a day before you migrate, and leave the old mailboxes reachable for a few days afterwards so nothing in flight is lost.
Can I have MX records at two providers at once?
You can, but it rarely does what people expect. Equal priorities split incoming mail between them, so messages end up scattered across two systems. Use priority to make one a genuine fallback, or complete the migration and remove the old records.