b.ns.srv.cr has no MX records.
Question and response
Question
dig b.ns.srv.cr. MX
Answer
The response has no answer records.
Authority
srv.cr. 1800 SOA audrey.ns.cloudflare.com. dns.cloudflare.com. 2395263820 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0