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 service provider. On their end, three records are created automatically as soon as the Internet domain is added - one A record and two MX records. The former is a numeric address, or IP address, which “tells” the domain name where its website is, while the other two are alphanumeric and they reveal the server that handles the e-mails for that specific domain address. The site and the e-mail hosting are often perceived as one thing, when they are in reality two different services. Having independent records for them will enable you to have them with different companies if you wish. As an example, some new company might have excellent uptime for your website, but you may not want to switch your e-mails from your current host and by using an A record to point the domain name to the former and MX records to have the e-mails with the latter, you will get the best of both providers. These records are checked when you wish to open a website or send an email - in any case, the provider whose name servers are used for the domain is going to be contacted to retrieve the A and MX records and if you've set records different from their own, the correct web/mail server will then be contacted and you're going to see the needed website or your e-mail will be delivered.