What are MX records and how it should look?
MX is the short name for "Mail Exchanger", this is the type of DNS (Domain Name System) record. DNS is the key to a service for a domain. The mail server that sends an email message looks up for MX records for destination domain to find destination mail server.
MX DNS record looks the following way:
# dig mx google.com
;; ANSWER SECTION:
google.com. 585 IN MX 30 alt2.aspmx.l.google.com.
google.com - destination domain name.
MX - record type.
30 - priority of mail server.
alt2.aspmx.l.google.com - mail server name.
585 IN - Service information, such as TTL. Not a part of MX DNS record.