Apex domains cannot have CNAME records.
Question and response
Question
dig mails.qualitia.com. NS
Answer
mails.qualitia.com. 5 NS ns-732.awsdns-27.net.
mails.qualitia.com. 5 NS ns-85.awsdns-10.com.
mails.qualitia.com. 5 NS ns-1846.awsdns-38.co.uk.
mails.qualitia.com. 5 NS ns-1074.awsdns-06.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0