imap1.us.opalstack.com has no CNAME records.
Question and response
Question
dig imap1.us.opalstack.com. NS
Answer
The response has no answer records.
Authority
opalstack.com. 75 SOA ns3.us.opalstack.com. hostmaster.opalstack.com. 2026021703 10800 300 1814400 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0