A Mail Exchanger Record ( MX Record )
MX Record stands for the Mail Exchanger Record in the DNS Records.
It is responsible for the e-mail exchanges in a domain.
It specifies a mail server on which mails can be received of that domain.
When a request is made to send an e-mail, the server finds for the MX Record. To tell the name of mail server on to which the mail has to be send, and after that the mail is sent to the server.
Therefore, MX Record plays a very crucial role in e-mail exchanges. So it is nearly impossible to to do mail exchange without having MX Record.