When you add a domain name as hosted in some account, you normally set a pair of Name Servers to point it to that specific service provider. On their end, three records are created automatically when 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 address where its website is, while the other two are alphanumeric and they reveal the server that manages the e-mails for that particular domain name. The website and the email hosting are generally considered to be one thing, when they're in fact two different services. Having independent records for them will permit you to have them with different companies if you wish. As an example, some new provider could have fantastic uptime for your site, but you may not want to switch your e-mail messages from your current host and by using an A record to point the domain name to the former and MX records to have the emails with the second, you can get the best of both companies. These records are checked when you want to open a site or send an e-mail - in either case, the provider whose name servers are used for the Internet domain 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 e-mail is going to be delivered.