mx0.firedrake.org has no CNAME records.
Question and response
Question
dig mx0.firedrake.org. NS
Answer
The response has no answer records.
Authority
firedrake.org. 3498 SOA firedrake.org. hostmaster.firedrake.org. 3443716143 21600 10800 604800 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0