Which application protocol rules the mail service?

Ok, when a mail is to be transferred over a network and has a certain domain for a destination, how do servers pass this mail to the right server? I've read that if the intermediate server doesn't have the destination in record, it passes the mail to the next MTA, which could have that record. In this process of finding the destination server, is there DNS protocol involved or does SMTP take care of passing mail to the right MTA?



Thanks for the answer!Which application protocol rules the mail service?
When you send email, the email server queries DNS to resolve the recipient's domain. During that check, the DNS server returns an MX record which essentially tells the server what IP address or addresses are responsible for handling incoming email for that domain. At that point your email server or MTA will open an SMTP connection to the recipient's email server or MTA and delivers the message. This is a pretty simplified explanation that doesn't explain what happens when your local DNS server doesn't have a cached entry for that domain or what happens when a domain has multiple MX records, but you get the point.