4.authorize.certificatemanager.goog has no MX records.
Question and response
Question
dig 4.authorize.certificatemanager.goog. MX
Answer
The response has no answer records.
Authority
4.authorize.certificatemanager.goog. 60 SOA ns-cloud-b1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 60
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0