MX · RFC 5321
MX Record Lookup
See which servers receive email for a domain, in the order senders try them, with their addresses, the detected email provider and any configuration problems.
Lookup
How MX records work
When someone sends mail to you@example.com, their server asks DNS for the MX records of example.com and tries the hosts in order of priority, lowest number first. Hosts with the same priority share the load. This lookup lists them in that order and resolves the A (IPv4) and AAAA (IPv6) addresses of every host.
Provider detection
The provider is recognised from the host names: Google Workspace, Microsoft 365, Zoho, Proton, Fastmail, iCloud, Yandex, Cloudflare Email Routing, Amazon SES and WorkMail, and security gateways such as Mimecast, Proofpoint, Barracuda or Cisco. A gateway in front of a mailbox provider hides the provider, because the gateway is what receives the mail first.
Problems it detects
- Null MX (
0 .): the domain declares that it accepts no email (RFC 7505). Correct for parked domains, a mistake when mixed with other MX records. - CNAME targets: an MX host must not be an alias (RFC 2181).
- Missing hosts: MX names without an address cannot receive mail.
- IP addresses and private ranges in MX records, which senders refuse or cannot reach.
Frequently asked questions
What does the MX priority number mean?
Lower numbers are tried first. Senders only use a higher-numbered server when the lower ones do not answer, and servers with equal numbers share the load.
What happens if a domain has no MX record?
Senders fall back to the domain’s own A or AAAA address, which is called an implicit MX. If no mail server listens there, messages bounce. Domains that should never receive mail can publish a null MX instead.
Why should an MX record not point to a CNAME?
RFC 2181 forbids it, and RFC 5321 expects the MX target to be a host name with its own address records. Most large senders follow the alias anyway, but some do not, so mail can be lost.
Can MX records tell me who hosts a domain’s email?
Usually, for the large providers listed above. Self-hosted servers and smaller hosts use their own names, so no provider is shown for them.