The help article doesn’t mention MX anywhere on it. MX records are used to set up domains for receiving emails, they tell the internet which server to send mail to. More info here: https://www.cloudflare.com/en-gb/learning/dns/dns-records/dns-mx-record/
We at our current implementation in Qualtrics & looking at the name of the record for Qualtrics the MX is used for bounces, so their system must track and do something with the returned emails.
The record is only for receiving email, but it is often used by receiving mail systems to check the sender for spam too. It’s easy to send emails, often harder to have proper MX records set up to show the mailbox is a receiver too.
Our main email vendor is Sendgrid, their docs for the same process regarding record setup is here: https://www.twilio.com/docs/sendgrid/ui/account-and-settings/how-to-set-up-domain-authentication
How does QuestionPro intend to handle the bounces?