mta-tw-080.gca.su has no CNAME records.
Question and response
Question
dig mta-tw-080.gca.su. NS
Answer
The response has no answer records.
Authority
gca.su. 715 SOA ns-mail01.getcourse.ru. hostmaster.gca.su. 1438 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0