Apex domains cannot have CNAME records.
Question and response
Question
dig transmail.com. NS
Answer
transmail.com. 5 NS dns3.p03.nsone.net.
transmail.com. 5 NS pdns90.ultradns.com.
transmail.com. 5 NS ns1.zohocorp.com.
transmail.com. 5 NS pdns90.ultradns.net.
transmail.com. 5 NS pdns90.ultradns.org.
transmail.com. 5 NS dns2.p03.nsone.net.
transmail.com. 5 NS pdns90.ultradns.biz.
transmail.com. 5 NS dns1.p03.nsone.net.
Authority
The response has no authority records.
Additional
dns1.p03.nsone.net. 1 A 198.51.44.3
dns2.p03.nsone.net. 1 A 198.51.45.3
dns3.p03.nsone.net. 1 A 198.51.44.67
dns1.p03.nsone.net. 1 AAAA 2620:4d:4000:6259:7:3:0:1
dns2.p03.nsone.net. 1 AAAA 2a00:edc0:6259:7:3:0:0:2
dns3.p03.nsone.net. 1 AAAA 2620:4d:4000:6259:7:3:0:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0