oxygen.clearfly.io has no MX records.
Question and response
Question
dig oxygen.clearfly.io. MX
Answer
The response has no answer records.
Authority
clearfly.io. 3600 SOA ns1.as72400.net. sysops.as27400.net. 2026020201 10800 900 1814400 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0