Networking Fundamentals Practice Question 4: DNS Mail Record
Networking Fundamentals · Test 1 · question 4 of 10
A small company owns the domain example.com and has moved its email to a hosted mail server named mail.example.net. Other mail servers on the Internet must learn where to deliver messages addressed to anyone@example.com. Which DNS record should be added to the example.com zone?
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Answer:
An MX (mail exchange) record names a host that is willing to accept mail for the domain. It also has a preference value, where lower is preferred, so a domain can list backup mail servers. Sending mail servers look up the MX record for example.com to decide where to deliver. So C is correct.
- A. An A record maps a name to an IPv4 address. Pointing example.com's A record at the mail server would send *all* traffic for example.com, including the website, to the mail server, and it still wouldn't tell senders that this host handles mail. - B. An AAAA record is the IPv6 equivalent of an A record, so it has the same problem. - D. A CNAME makes a name an alias of another name. A CNAME can't share its name with other records, and the zone apex (example.com) always has SOA and NS records, so a CNAME there is not allowed. It also would not mark the target as a mail exchange.
References: RFC 1035 - Domain Names: Implementation and Specification, sections 3.3.1 and 3.3.9; RFC 1034 - Domain Names: Concepts and Facilities, section 3.6.2