This does not go over DNS for email, which is different. And I’m not even sure how that DNS data is looked up, for mail-relay. SMTP and IMAP use the regular A and CNAME records. The MX record, is used for relay, from the SMTP endpoint, to send to the IMAP endpoint. Other than that basic idea, I’m unfamiliar with the mechanism there. This record is something you will need to manipulate (or your mail provider), if you subscribe to Microsoft 365 (or other cloud SaaS mail services). Microsoft 365, is a monthly subscription to office products served over internet, and one of its products is a mail server with your own email address, which uses that MX record. This is what we did in our Exchange class in BCIT, but there wasn’t a lot of in-depth description of what protocols or mechanisms that use those DNS entries. So I know you need them, and that is all.