mail4.visionflow.com has no NS records.
NS records for this zone are defined at visionflow.com.
NS records for this zone are defined at visionflow.com.
Question and response
Question
dig mail4.visionflow.com. NS
Answer
The response has no answer records.
Authority
visionflow.com. 3600 SOA ns1.loopia.se. registry.loopia.se. 1773273600 14400 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0