mail.serverastra.com has no NS records.
NS records for this zone are defined at serverastra.com.
NS records for this zone are defined at serverastra.com.
Question and response
Question
dig mail.serverastra.com. NS
Answer
The response has no answer records.
Authority
serverastra.com. 300 SOA dns1.serverastra.com. hostmaster.serverastra.com. 2026020902 1000 600 86400 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0