Apex domains cannot have CNAME records.
Question and response
Question
dig send.fakturownia.pl. NS
Answer
send.fakturownia.pl. 5 NS ns-a-2.getresponse360.pl.
send.fakturownia.pl. 5 NS ns-a-1.getresponse360.pl.
Authority
The response has no authority records.
Additional
ns-a-1.getresponse360.pl. 5 A 104.160.66.146
ns-a-2.getresponse360.pl. 5 A 178.16.117.237
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0