hs01a.dkim.hubspotemail.net has no MX records.
Question and response
Question
dig hs01a.dkim.hubspotemail.net. MX
Answer
The response has no answer records.
Authority
hs01a.dkim.hubspotemail.net. 180 SOA ns10.digicertdns.com. dns.digicertdns.com. 2048126419 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0