Name server MX record

Mail Exchanger Record (MX record) is a type of resource in the nameserver system that allows specifying the server responsible for delivering email for a particular domain.
If multiple email servers are used, prioritization can be applied based on the settings in the MX record (priority is indicated with a number—the smaller the number, the higher the priority).
In summary, the MX record in the nameserver defines how and where to route emails using the SMTP (Simple Mail Transfer Protocol).