smtpblk.tes.com.pk has no CNAME records.
Question and response
Question
dig smtpblk.tes.com.pk. NS
Answer
The response has no answer records.
Authority
tes.com.pk. 4082 SOA tes.com.pk. hostmaster.tes.com.pk. 2025123114 21600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0