mail.posti.com has no NS records.
NS records for this zone are defined at posti.com.
NS records for this zone are defined at posti.com.
Question and response
Question
dig https://outlook.com/posti.com. NS
Answer
The response has no answer records.
Authority
com. 900 SOA a.gtld-servers.net. nstld.verisign-grs.com. 1771848366 1800 900 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0