Apex domains cannot have CNAME records.
Question and response
Question
dig mastercard-email.com. NS
Answer
mastercard-email.com. 5 NS a26-66.akam.net.
mastercard-email.com. 5 NS a9-64.akam.net.
mastercard-email.com. 5 NS dns1.mastercard.com.
mastercard-email.com. 5 NS dns2.mastercard.com.
mastercard-email.com. 5 NS a1-29.akam.net.
mastercard-email.com. 5 NS a7-67.akam.net.
mastercard-email.com. 5 NS a18-64.akam.net.
mastercard-email.com. 5 NS a22-65.akam.net.
Authority
The response has no authority records.
Additional
a1-29.akam.net. 5 A 193.108.91.29
a7-67.akam.net. 5 A 23.61.199.67
a9-64.akam.net. 5 A 184.85.248.64
a18-64.akam.net. 5 A 95.101.36.64
a22-65.akam.net. 5 A 23.211.61.65
a26-66.akam.net. 5 A 23.74.25.66
a1-29.akam.net. 5 AAAA 2600:1401:2:0:0:0:0:1d
a7-67.akam.net. 5 AAAA 2600:1406:32:0:0:0:0:43
a9-64.akam.net. 5 AAAA 2a02:26f0:117:0:0:0:0:40
a18-64.akam.net. 5 AAAA 2600:1480:4800:0:0:0:0:40
a22-65.akam.net. 5 AAAA 2600:1480:7800:0:0:0:0:41
a26-66.akam.net. 5 AAAA 2600:1480:b800:0:0:0:0:42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0