Senders cannot deliver mail to a university domain. Public DNS for that domain has address records and no mail-exchanger record. Which record should be added?
Select an answer to reveal the explanation.
Short Explanation
People can find the building, and the mailbox has no label, so the letters you send never arrive. The label for inbound mail is an MX record pointing at the host that accepts it. A reverse name, a website alias, and a router advertisement do not tell the rest of the world where to deliver mail.
Full Explanation
An MX record names the host that accepts email for a domain. The university has address records and no mail-exchanger record, and senders cannot deliver mail, so the missing MX is the record to add. A PTR record is the reverse mapping from an address to a name. Receiving sites often check the sender's PTR. It does not publish where inbound mail for your domain should go. A CNAME aliases one name to another, commonly for a website. It is not the record senders use to find a mail exchanger. SLAAC lets an IPv6 host build an address from a router advertisement. It does not write DNS mail records. Exam caveat: the host named by the MX also needs an address record. An MX that points at a name with no address still fails. Operational check: add the MX toward the mail host, confirm that name has an address record, and send a test message from outside the university. Send the test from a network outside the university so you are not fooled by an internal relay that ignores public DNS. Confirm the MX preference if you publish more than one mail host.