b.ns.lb has no MX records.
Question and response
Question
dig b.ns.lb. MX
Answer
The response has no answer records.
Authority
lb. 172800 SOA b.ns.lb. hostmaster.psg.com. 1771397633 86400 3600 2592000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0