When 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, 3 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, that “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 specific Internet domain. The website and the email hosting are typically considered to be one thing, when they are in reality two different services. Having different records for them will enable you to have them with different companies if you wish. For instance, some new service provider might 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 emails with the latter, you can get the best of both providers. These records are checked when you wish to open a website or send an e-mail - either way, the company 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're going to see the needed site or your e-mail will be delivered.