A description of DNS server functionality, and the steps required to remove a domain from one.
What is a DNS server?
DNS (Domain Name System) is the protocol that is used by computer networks to translate IP (Internet Protocol) addresses into domain names. A DNS server is a computer specifically set up to be queried by other computers for the IP-to-domain translations. There are many kinds of records that can be associated with a specific domain name, but the ones of primary interest for this document are A records (used to point websites to the computers that host them) and MX records (used to point email to their appropriate server). The result of a DNS query is a resolved IP address. Every time a web page is loaded or an email is sent, at least one DNS query has resolved by a DNS server.
What is required to remove a listed domain?
For a DNS server to stop answering for a domain, records associated with the specific domain must be removed from the list of records the DNS server has. In most situations, the minimum numbers of records associated with a domain for a website and email to function is 4. One record for each of the following:
1. A record domain.com XXX.XXX.XXX.XXX (ip address)
2. A record www.domain.com XXX.XXX.XXX.XXX (ip address)
3. MX record domain.com {name of email server} {priority 1}
4. MX record domain.com {name of email different server} {priority 2}8
How can having incorrect DNS entries affect domain and email queries?
When a potential contact sends an email to a company with a hosted email service ({user}@domain.com), the email leaves the client machine (by email client such as Outlook, or web client such as Gmail) and arrives at their email server for processing. First, the email server checks itself to see if it is the destination. If it is the destination server, the email gets delivered to the appropriate domain and account. Otherwise, the email server then performs a DNS query and resolves the address of the hosted email server and delivers the message to it.
When a queried server does not answer for a domain, it should return a result of Unknown or Failed. When a queried server knows the result, it returns the requested record type.