Whenever you add a domain as hosted in some account, you normally set a pair of Name Servers to direct it to that specific provider. On their end, three records are created automatically the moment the domain name is added - one A record and two MX records. The former is a numeric address, or IP address, which “tells” the domain name where its site is, while the other two are alphanumeric and they reveal the server that manages the e-mails for that particular domain name. The site and the email hosting are generally considered to be one thing, while they are in reality two different services. Having different records for them will enable you to have them with different providers if you wish. For example, some new company might have exceptional uptime for your site, but you might 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 latter, you could get the best of both providers. These records are checked when you want to open a site or send an e-mail - either way, the company 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 are going to see the needed site or your e-mail will be delivered.