sb.nexlinx.net.pk has no MX records.
Question and response
Question
dig sb.nexlinx.net.pk. MX
Answer
The response has no answer records.
Authority
nexlinx.net.pk. 10 SOA pathfinder.nexlinx.net.pk. root.nexlinx.net.pk. 2018101149 500 1800 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0