mailserver.libware.pt has no NS records.
NS records for this zone are defined at libware.pt.
NS records for this zone are defined at libware.pt.
Question and response
Question
dig mailserver.libware.pt. NS
Answer
The response has no answer records.
Authority
libware.pt. 1800 SOA ns2.no-ip.com. hostmaster.no-ip.com. 2015030523 10800 1800 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0