ns.rightsdns.com has no MX records.
Question and response
Question
dig ns.rightsdns.com. MX
Answer
The response has no answer records.
Authority
rightsdns.com. 856 SOA ns.rightsdns.com. root.rightsdns.com. 2021081000 3600 1200 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0