a.ns.shopco.com has no MX records.
Question and response
Question
dig a.ns.shopco.com. MX
Answer
The response has no answer records.
Authority
shopco.com. 60 SOA a.ns.shopco.com. hostmaster.shopco.com. 2024052300 10800 3600 2592000 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0