MX records are responsible for providing the correct routing information for incoming mail of a domain.
For example, when a friend of yours sends an email to your domain, massivedns.com, your friend will lookup the MX records of the domain to find the correct location of your mail server.
Please be aware that an MX record must not contain an IP address, it must be a FQDN / Hostname (i.e. mail.massivedns.com or massivedns.com)
This can be achieved by creating an A record for massivedns.com or mail.massivedns.com, and then pointing your MX records to either location.