When you add a domain name as hosted in some account, you normally set a pair of Name Servers to direct it to that specific service provider. On their end, three records are set up automatically right after the domain address is added - one A record and two MX records. The former is a numeric address, or IP address, which “tells” the Internet domain where its website is, while the other two are alphanumeric and they show the server that manages the emails for that particular domain name. The site and the email hosting are often thought to be one thing, while they're in reality two different services. Having separate records for them will allow you to have them with different providers if you would like. For example, some new service provider may have outstanding uptime for your site, but you may not want to switch your emails from your current host and by employing an A record to point the domain name to the former and MX records to have the emails with the second, you will get the best of both providers. These records are checked when you wish to open a website or send an e-mail - either way, the service provider whose name servers are used for the Internet domain will be contacted to retrieve the A and MX records and if you've set records different from their own, the right web/mail server will then be contacted and you will see the needed site or your email is going to be delivered.