When you add a domain name as hosted in some account, you normally set a pair of Name Servers to direct it to that specific service provider. On their end, three records are created automatically the moment the domain is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the Internet domain where its site is, while the other two are alphanumeric and they indicate the server that manages the emails for that specific domain address. The website and the email hosting are often considered to be one thing, when they are in fact two different services. Having separate records for them will permit you to have them with different companies if you wish. For instance, some new company can have outstanding uptime for your site, but you might not want to switch your emails from your current host and by employing an A record to point the domain to the first and MX records to have the e-mails with the second, you could get the best of both companies. These records are checked when you wish to open a website or send an e-mail - in any case, the service provider whose name servers are used for the domain address is going to be contacted to retrieve the A and MX records and if you have 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 email will be delivered.