Whenever you add a domain as hosted in some account, you normally set a pair of Name Servers to point it to that particular company. 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 name where its site is, while the other two are alphanumeric and they show the server that manages the emails for that specific domain name. The website and the email hosting are usually considered to be one thing, while they are in reality two different services. Having independent records for them will allow you to have them with different companies if you would like. For example, some new service provider can have excellent uptime for your site, but you may 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 e-mails with the second, you will get the best of both providers. These records are checked when you want to open a website or send an e-mail - in any case, the 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 right web/mail server will then be contacted and you will see the needed site or your e-mail is going to be delivered.