Any time you add a domain as hosted in some account, you usually set a pair of Name Servers to point it to that specific company. On their end, three records are created automatically when the domain address is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the Internet domain where its site is, while the other two are alphanumeric and they show the server that manages the emails for that particular Internet domain. The website and the email hosting are often thought to be one thing, while they're actually two different services. Having separate records for them will enable you to have them with different companies if you would like. For example, some new company might have fantastic uptime for your site, but you might not want to switch your e-mails from your current host and by using an A record to point the domain to the first and MX records to have the emails with the latter, you will get the best of both companies. These records are checked when you want to open a site or send an email - in any case, the provider whose name servers are used for the domain name will be contacted to retrieve the A and MX records and if you've set records different from their own, the correct web/mail server will then be contacted and you'll see the needed site or your email will be delivered.