Any time you add a domain as hosted in some account, you typically 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 domain address is added - one A record and two MX records. The former is a numeric address, or IP address, which “tells” the domain where its website is, while the other two are alphanumeric and they reveal the server that manages the e-mails for that particular Internet domain. The site and the e-mail hosting are usually perceived as one thing, while they are in reality two different services. Having different records for them will enable you to have them with different companies if you would like. As an example, some new provider might have excellent uptime for your site, but you may not want to switch your emails from your current host and by employing an A record to point the domain to the first and MX records to have the emails with the second, you can get the best of both providers. These records are checked when you want to open a website or send an e-mail - in either case, the provider whose name servers are used for the domain name is going to 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're going to see the needed website or your email will be delivered.