Whenever you add a domain as hosted in some account, you usually set a pair of Name Servers to direct it to that particular provider. On their end, three records are set up automatically when 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 website is, while the other two are alphanumeric and they indicate the server that handles the emails for that particular domain. The website and the e-mail hosting are often thought to be one thing, while they're in fact two different services. Having different records for them will permit you to have them with different providers if you would like. For instance, 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 e-mails with the latter, you will 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 Internet domain 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 email is going to be delivered.