aspmx.pardot.com has no CNAME records.
Question and response
Question
dig aspmx.pardot.com. NS
Answer
The response has no answer records.
Authority
pardot.com. 203 SOA dns1.p06.nsone.net. hostmaster.nsone.net. 1666727972 3600 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0