Any time you add a domain as hosted in some account, you typically set a pair of Name Servers to direct it to that specific service provider. On their end, three records are created automatically right after the Internet 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 show the server that deals with the e-mails for that specific domain name. The site and the e-mail hosting are typically regarded as one thing, when they're in reality two different services. Having different records for them will allow you to have them with different providers if you'd like. As an example, some new provider can have superb uptime for your site, but you may not want to switch your e-mails from your current host and by using an A record to point the domain address to the former and MX records to have the e-mails with the latter, you can get the best of both providers. These records are checked when you wish to open a site or send an e-mail - either way, 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.