A DNS Registrar is authorized by ICANN to sell domain names. They essentially do the admin work required for the Domain Name System. Registrars have become important because they are private companies and they have started to become more political in their policies for maintaining clients for DNS services.
Subdomains are prefixes to domain names that allow administrators to provide different web services to users, but do so using the same namespace so that it is easier to remember. Such as MAIL.failednormal.com, WWW.failednormal.com, VPN.failednormal.com… […]
MX Records (Mail Exchange) are DNS records that are used to route email to email servers. You can have numerous MX Records posting to different email servers to prevent loss of email due to downtime. […]