mail.gruporscom.com has no CNAME records.
Question and response
Question
dig mail.gruporscom.com. NS
Answer
The response has no answer records.
Authority
gruporscom.com. 3342 SOA dns1.artinfo.com.br. postmaster.gruporscom.com. 2026011901 3600 1200 1728000 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0