Apex domains cannot have CNAME records.
Question and response
Question
dig zimbraTest.albedo.it. NS
Answer
zimbraTest.albedo.it. 5 NS dns2.albedo.it.
zimbraTest.albedo.it. 5 NS dns.albedo.it.
Authority
The response has no authority records.
Additional
dns.albedo.it. 5 A 81.201.0.2
dns2.albedo.it. 5 A 81.201.0.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0