When you add a domain name 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 set up automatically the moment the domain 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 site is, while the other two are alphanumeric and they reveal the server that deals with the e-mails for that particular domain name. The site and the email hosting are usually perceived as one thing, when they're in fact two different services. Having independent records for them will permit you to have them with different providers if you wish. As an example, some new company may have outstanding uptime for your website, but you might not want to switch your emails 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 latter, you can 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 service provider whose name servers are used for the Internet domain will 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 will see the needed site or your email will be delivered.