Any time you add a domain name as hosted in some account, you typically set a pair of Name Servers to point it to that particular 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 domain name where its site is, while the other two are alphanumeric and they show the server that handles the e-mails for that specific domain name. The website and the email hosting are typically regarded as one thing, while they're in reality two different services. Having independent records for them will enable you to have them with different providers if you wish. For instance, some new service provider may have exceptional uptime for your website, but you may not want to switch your emails from your current host and by using an A record to point the domain name to the former and MX records to have the e-mails with the second, you will get the best of both companies. These records are checked whenever you want to open a website or send an email - in any case, the service provider whose name servers are used for the domain name is going to 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 are going to see the needed website or your email will be delivered.