mx2.active24.com has no CNAME records.
Question and response
Question
dig mx2.active24.com. NS
Answer
The response has no answer records.
Authority
active24.com. 3419 SOA alfa.ns.active24.cz. hostmaster.active24.cz. 2025110406 10800 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0