MX lookup

An MX, or mail exchanger, record names a server that accepts email for a domain. Each has a priority number, and sending servers try the lowest number first, then fall back to higher ones if it does not answer.

Type the domain, or any email address on it, and press Look up. The tool asks a public DNS resolver for the MX records and lists them in the order servers will try them, with the email provider worked out from the host names.

Senders then try to deliver to the domain’s own A record, which usually fails. A domain that should never receive mail can publish a null MX record, a single MX of priority 0 pointing to a dot, to say so explicitly.

Google Workspace now uses one MX record, smtp.google.com with priority 1. Older setups list ASPMX.L.GOOGLE.COM and four ALT servers. Microsoft 365 uses one record ending in mail.protection.outlook.com, shown in the Microsoft 365 admin center.

Resolvers keep the old answer until its TTL runs out. Check the change with the DNS propagation checker, and keep the old mailbox running until every resolver shows the new records.