In ordr to create mail exchanger records for your domain (example.com) you have to
1- Create DNS record
Record type : A record
Name : mail.example.com
IP address : Public IP address of your email server or public ip address that forwards SMTP traffic to your email server
2- Create mail exchanger record
Record type : MX record
Name : mail
Mail server (Points to A record) : mail.example.com
Priority : A number between 0 and 65535 that indicates the mail exchange server’s priority with respect to the other mail exchange servers