mail.coolcatmail.com has no MX records.
Question and response
Question
dig mail.coolcatmail.com. MX
Answer
The response has no answer records.
Authority
coolcatmail.com. 900 SOA kiki.bunny.net. hostmaster.bunny.net. 2021375252 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0