Whenever you add a domain as hosted in some account, you typically set a pair of Name Servers to point it to that specific company. On their end, three records are set up automatically right after the domain address is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the Internet domain where its website is, while the other two are alphanumeric and they indicate the server that manages the e-mails for that particular domain. The website and the e-mail hosting are typically thought to be one thing, while they're actually two different services. Having separate records for them will permit you to have them with different providers if you would like. For instance, some new provider could have exceptional uptime for your website, but you may not want to switch your e-mail messages from your current host and by using an A record to point the domain name 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 want to open a site or send an e-mail - either way, the service provider whose name servers are used for the domain name will 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 website or your email is going to be delivered.