dns – rhel + resolve.conf + what is the right resolve.conf settings

we want to know what is the right configuration in resolve.conf and about domain name in resolve.conf

in our rhel 7 server we configured the following example of resolve.conf

more /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
search sandyam.com
nameserver 12.21.16.17
domain sandyam.com
but we can also set the following resolve.conf , without domain sandyam.com , and resolving will works fine

more /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
search sandyam.com
nameserver 12.21.16.17
or to set as the following without search sandyam.com , and resolving will works fine

more /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
nameserver 12.21.16.17
domain sandyam.com
so we are little not sure what is the right resolve.conf settings ( option 1 or option 2 or option 3 )

option 1

more /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
search sandyam.com
nameserver 12.21.16.17
domain sandyam.com
option 2

more /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
search sandyam.com
nameserver 12.21.16.17
option 3

more /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
nameserver 12.21.16.17
domain sandyam.com