www IN A 192.168.1.12
web IN CNAME www
MX record: Used to define where email should be sent to. Must point to an A record, not a CNAME.
IN MX mail.example.com.
mail IN A 192.168.1.13
NS record: Used to define which servers serve copies of a zone. It must point to an A record, not a CNAME. This is where Primary and Secondary servers are defined.
IN NS ns.example.com.
IN NS ns2.example.com.
ns IN A 192.168.1.10
ns2 IN A 192.168.1.11