Apex domains cannot have CNAME records.
Question and response
Question
dig mtaspb.email. NS
Answer
mtaspb.email. 5 NS ns-769.awsdns-32.net.
mtaspb.email. 5 NS ns-82.awsdns-10.com.
mtaspb.email. 5 NS ns-2033.awsdns-62.co.uk.
mtaspb.email. 5 NS ns-1227.awsdns-25.org.
Authority
The response has no authority records.
Additional
ns-82.awsdns-10.com. 2 A 205.251.192.82
ns-769.awsdns-32.net. 2 A 205.251.195.1
ns-1227.awsdns-25.org. 2 A 205.251.196.203
ns-2033.awsdns-62.co.uk. 2 A 205.251.199.241
ns-82.awsdns-10.com. 2 AAAA 2600:9000:5300:5200:0:0:0:1
ns-769.awsdns-32.net. 2 AAAA 2600:9000:5303:100:0:0:0:1
ns-1227.awsdns-25.org. 2 AAAA 2600:9000:5304:cb00:0:0:0:1
ns-2033.awsdns-62.co.uk. 2 AAAA 2600:9000:5307:f100:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0