What must be true in the DNS setup to establish load sharing via DNS round robin across
multiple SMTP gateway servers?

A.
the Ptr records for the servers must point to the same hostname

B.
the load sharing attribute must reference a valid hardware load balancer with an
externally routable IP address

C.
the preference numbers or weightings of the MX records must be the same

D.
the preference numbers of the A records must be set to 10