Any time you add a domain name 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 former is a numeric address, or IP address, which “tells” the domain address where its site is, while the other two are alphanumeric and they reveal the server that handles the emails for that particular domain name. The site and the email hosting are often perceived as one thing, when they are in reality two different services. Having independent records for them will enable you to have them with different companies if you wish. As an illustration, some new provider may have excellent uptime for your site, but you might not want to switch your e-mails from your current host and by using an A record to point the domain name to the first and MX records to have the emails with the second, you can get the best of both companies. These records are checked when you wish to open a site or send an e-mail - in any case, the 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've set records different from their own, the right web/mail server will then be contacted and you're going to see the needed site or your email is going to be delivered.