Whenever you add a domain as hosted in some account, you typically set a pair of Name Servers to direct it to that specific service provider. On their end, three records are set up 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 indicate the server that manages the emails for that particular domain address. The site and the email hosting are often perceived as one thing, when they are in reality two different services. Having independent records for them will allow you to have them with different companies if you wish. For instance, some new service provider can have outstanding uptime for your website, but you may not want to switch your emails from your current host and by using an A record to point the domain to the first and MX records to have the emails with the second, you will get the best of both companies. These records are checked whenever you want to open a site or send an email - either way, the company whose name servers are used for the Internet domain 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 will see the needed site or your e-mail will be delivered.