dc31.zaptail.com has no CNAME records.
Question and response
Question
dig dc31.zaptail.com. NS
Answer
The response has no answer records.
Authority
zaptail.com. 721 SOA ns1.dnsexit.com. admin.netdorm.com. 2000060701 86000 180000 1814400 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0