Glossary · DNS
An MX record tells the internet which servers accept email for a domain, with a priority number to set the order they're tried in.
Each MX record has a priority and a hostname; lower numbers are tried first, and equal numbers share the load. MX records must point to hostnames (with their own A or AAAA records), not to IP addresses or CNAME aliases.
Changing MX records is what moves inbound mail to a new provider. A domain that sends no mail can publish a null MX, a single record of 0 . (RFC 7505), so senders know not to try.
acme.com. MX 10 mx1.mailhost.example.
acme.com. MX 20 mx2.mailhost.example.Every domain you run in one inbox, from $3 a mailbox. 14 days free, no card.