b.nic.mx has no MX records.
Question and response
Question
dig b.nic.mx. MX
Answer
The response has no answer records.
Authority
nic.mx. 300 SOA a.nic.mx. hostmaster.nic.mx. 2025090301 3600 900 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0