MX Lookup

An MX (Mail Exchanger) record is a DNS record that specifies which mail servers are responsible for accepting email for a domain. When someone sends email to user@example.com, the sending server performs an MX lookup to find the mail server hostname, then connects to it to deliver the message. A domain can have multiple MX records with different priority values for redundancy.

The priority number (also called preference) tells sending mail servers which MX host to try first — lower numbers have higher priority. For example, a server with priority 10 is preferred over one with priority 20. If the highest-priority server is unavailable, the sending server tries the next one. Setting two MX records with the same priority distributes load equally between them.

Yes, but it affects how email is delivered. Without an MX record, sending servers fall back to the domain's A record (if one exists) and attempt delivery there. This is called the implicit MX fallback. For domains that should never receive email, it is best practice to publish a null MX record: a single MX record with priority 0 and a dot as the target (example.com. 3600 IN MX 0 .) to explicitly refuse email delivery.

MX record results can differ by location due to DNS propagation delays after a recent change, DNS caching where resolvers serve a cached (older) answer until the TTL expires, or GeoDNS configurations that intentionally return different records based on the query origin. Use a DNS propagation checker to verify that your new MX records have propagated globally.