Any time you add a domain as hosted in some account, you typically set a pair of Name Servers to direct it to that particular service provider. On their end, three records are created automatically right after the domain name is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the domain where its site is, while the other two are alphanumeric and they show the server that handles the e-mails for that particular domain name. The site and the e-mail hosting are generally considered to be one thing, when they are actually two different services. Having independent records for them will allow you to have them with different providers if you want. For instance, some new company might have excellent uptime for your website, but you might not want to switch your e-mail messages from your current host and by using an A record to point the domain to the former and MX records to have the e-mails with the second, you can get the best of both providers. These records are checked when you wish to open a site or send an email - in any case, the provider whose name servers are used for the Internet domain is going to be contacted to retrieve the A and MX records and if you have set records different from their own, the right web/mail server will then be contacted and you are going to see the needed website or your email will be delivered.