Whenever you add a domain name 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 the moment the Internet domain is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the domain where its site is, while the other two are alphanumeric and they reveal the server that deals with the emails for that specific domain. The site and the email hosting are usually regarded as one thing, when they are in fact two different services. Having different records for them will enable you to have them with different providers if you'd like. For instance, some new service provider can have superb uptime for your site, but you may not want to switch your e-mails from your current host and by employing an A record to point the domain address to the first and MX records to have the emails with the latter, you could get the best of both companies. These records are checked whenever you want to open a website or send an email - in any case, the company whose name servers are used for the domain 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'll see the needed site or your e-mail is going to be delivered.