mail.hikvision.com has no TXT records.
Question and response
Question
dig mail.hikvision.com. TXT
Answer
The response has no answer records.
Authority
hikvision.com. 180 SOA ns3.dnsv5.com. enterprise3dnsadmin.dnspod.com. 1772915150 3600 180 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0