pve.kookoolkan.com has no MX records.
Question and response
Question
dig pve.kookoolkan.com. MX
Answer
The response has no answer records.
Authority
kookoolkan.com. 60 SOA dns200.anycast.me. tech.ovh.net. 2026021800 86400 3600 3600000 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0