Any time you add a domain as hosted in some account, you typically set a pair of Name Servers to direct it to that specific provider. On their end, three records are created automatically as soon as the domain address 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 indicate the server that manages the e-mails for that specific Internet domain. The site and the e-mail hosting are typically regarded as one thing, when they are in fact two different services. Having independent records for them will allow you to have them with different companies if you'd like. As an example, some new service provider might have outstanding uptime for your website, but you might 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 e-mails with the latter, you can get the best of both providers. These records are checked when you wish to open a site or send an email - in either case, the service provider 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 will see the needed site or your email is going to be delivered.