Whenever you add a domain as hosted in some account, you normally set a pair of Name Servers to direct it to that particular service provider. On their end, 3 records are created automatically when 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 name where its site is, while the other two are alphanumeric and they indicate the server that manages the emails for that particular Internet domain. The website and the e-mail hosting are typically perceived as one thing, while they're in reality two different services. Having different records for them will allow you to have them with different providers if you wish. For instance, some new company may have superb 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 second, you will get the best of both companies. These records are checked whenever you want to open a website or send an e-mail - in either case, the service provider whose name servers are used for the 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'll see the needed site or your email will be delivered.