Whenever you add a domain name as hosted in some account, you usually set a pair of Name Servers to point it to that particular service provider. On their end, three records are set up automatically the moment the domain is added - one A record and two MX records. The first one is a numeric address, or IP address, that “tells” the Internet domain where its site is, while the other two are alphanumeric and they reveal the server that handles the emails for that particular domain name. The site and the e-mail hosting are often considered to be one thing, when they are in fact two different services. Having different records for them will allow you to have them with different companies if you'd like. For instance, some new provider may have exceptional uptime for your website, but you may not want to switch your e-mails from your current host and by employing an A record to point the Internet domain to the former and MX records to have the e-mails with the second, you could get the best of both providers. 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 name is going to be contacted to retrieve the A and MX records and if you have set records different from their own, the correct web/mail server will then be contacted and you are going to see the needed site or your email will be delivered.