When you add a domain name 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 set up automatically when the domain name is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the domain name where its website is, while the other two are alphanumeric and they show the server that manages the e-mails for that specific domain address. The site and the email hosting are often considered to be one thing, when they're in fact two different services. Having different records for them will permit you to have them with different providers if you wish. As an illustration, some new service provider could have outstanding uptime for your website, but you may not want to switch your e-mails 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 could get the best of both providers. These records are checked when you wish to open a site or send an e-mail - in any case, the service provider whose name servers are used for the domain will be contacted to retrieve the A and MX records and if you have set records different from their own, the right web/mail server will then be contacted and you are going to see the needed website or your e-mail will be delivered.