Any time you add a domain as hosted in some account, you usually set a pair of Name Servers to point it to that particular provider. On their end, 3 records are created automatically the moment the domain is added - one A record and two MX records. The former is a numeric address, or IP address, which “tells” the Internet domain where its site is, while the other two are alphanumeric and they show the server that manages the e-mails for that particular domain name. The site and the email hosting are generally regarded as one thing, while they're in fact two different services. Having independent records for them will allow you to have them with different providers if you would like. As an illustration, some new service provider may have excellent uptime for your site, but you might not want to switch your e-mails from your current host and by employing 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 companies. These records are checked whenever you want to open a site or send an email - either way, the service provider whose name servers are used for the domain address will 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're going to see the needed site or your e-mail is going to be delivered.