lustrous.firedrake.org has no MX records.
Question and response
Question
dig lustrous.firedrake.org. MX
Answer
The response has no answer records.
Authority
firedrake.org. 3600 SOA firedrake.org. hostmaster.firedrake.org. 3443716143 21600 10800 604800 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0