ns8.grupow.com.br has no MX records.
Question and response
Question
dig ns8.grupow.com.br. MX
Answer
The response has no answer records.
Authority
grupow.com.br. 3600 SOA ns10.grupow.com.br. atendimento.grupow.com.br. 1764010532 3600 3600 3600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0