DNS - MX record (Mail Exchanger Record)

The MX DNS is a DNS record that is defining a email server. You can only use one mail exchange server at a time.

The name of the MX record is the last part of an email address and design the host where the email should be delivered.

When an email is send, the server (MTA) sending the email lookups the MX record to find out the destination server.

When you add multiple MX records, the servers they point to must belong to the same service provider.

You can query them. For instance, the mail server of gmail can be found with the following nslookup command

nslookup -type=MX gmail.com

gmail.com       MX preference = 10, mail exchanger = alt1.gmail-smtp-in.l.google.com
gmail.com       MX preference = 20, mail exchanger = alt2.gmail-smtp-in.l.google.com
gmail.com       MX preference = 5, mail exchanger = gmail-smtp-in.l.google.com
gmail.com       MX preference = 40, mail exchanger = alt4.gmail-smtp-in.l.google.com
gmail.com       MX preference = 30, mail exchanger = alt3.gmail-smtp-in.l.google.com