When you add a domain as hosted in some account, you normally set a pair of Name Servers to point it to that particular provider. On their end, 3 records are set up automatically as soon as the domain name is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the domain name where its website is, while the other two are alphanumeric and they indicate the server that handles the e-mails for that particular domain. The website and the email hosting are generally thought to be one thing, while they are in reality two different services. Having separate records for them will enable you to have them with different providers if you want. For example, some new provider may have excellent uptime for your site, but you might not want to switch your e-mail messages from your current host and by employing an A record to point the domain address to the first and MX records to have the emails with the second, you could get the best of both companies. These records are checked when you want to open a website or send an email - either way, the company whose name servers are used for the domain address 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 site or your email is going to be delivered.