mx.sys.sulinet.hu has no CNAME records.
Question and response
Question
dig mx.sys.sulinet.hu. NS
Answer
The response has no answer records.
Authority
sys.sulinet.hu. 6595 SOA ns2.iif.hu. hostmaster.iif.hu. 2026021901 43200 14400 2592000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0