_dmarc.theory7.net has no CNAME records.
Question and response
Question
dig _dmarc.theory7.net. NS
Answer
The response has no answer records.
Authority
theory7.net. 3354 SOA dns.theory7.net. hostmaster.theory7.net. 2026020504 10800 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0