Any time you add a domain 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 name is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the Internet domain where its site is, while the other two are alphanumeric and they indicate the server that handles the e-mails for that particular domain address. The website and the email hosting are typically thought to be one thing, while they're in fact two different services. Having different records for them will allow you to have them with different companies if you'd like. As an example, some new service provider may have outstanding uptime for your website, but you may not want to switch your e-mail messages from your current host and by using an A record to point the domain address to the former and MX records to have the emails with the latter, you could get the best of both providers. 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 address is going to 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're going to see the needed website or your e-mail is going to be delivered.