When you add a domain name as hosted in some account, you usually set a pair of Name Servers to point it to that specific provider. On their end, 3 records are set up automatically the moment the domain address 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 show the server that manages the e-mails for that particular domain name. The site and the e-mail hosting are usually considered to be one thing, while they are in reality two different services. Having different records for them will permit you to have them with different providers if you want. For instance, some new company might have superb uptime for your website, but you may not want to switch your emails from your current host and by employing an A record to point the domain name to the first and MX records to have the emails with the latter, you will get the best of both companies. These records are checked when you wish to open a website or send an e-mail - in any case, the company 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 e-mail will be delivered.