smtp.dslplus.net.pk has no CNAME records.
Question and response
Question
dig smtp.dslplus.net.pk. NS
Answer
The response has no answer records.
Authority
dslplus.net.pk. 10800 SOA ns.link.net.pk. hostmaster.link.net.pk. 2019010905 10800 7200 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0