mx.klaviyo-site.com has no CNAME records.
Question and response
Question
dig mx.klaviyo-site.com. NS
Answer
The response has no answer records.
Authority
klaviyo-site.com. 2268 SOA dns.klaviyo-site.com. hostmaster.klaviyo-site.com. 1498300231 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0