I will give an example of adding MX records in the DNS settings of a domain name registrar.
The MX record determines who accepts mail for the specified domain, for example, for the ixnfo.com domain, accepts mail.ixnfo.com (you can call the mx.ixnfo.com subdomain or specify third-party email services like google, yandex, etc.):
Example MX record:
If there are several MX records, for example with priorities 10 and 20, then the record with the lowest priority (10) is selected first, if the server is not available, then the next record with the highest priority (20) is selected, if MX records with the same priority, then the selection is performed randomly.
See also my articles:
How to configure SPF records
Configure the PTR record on the DNS server