When you add a domain as hosted in some account, you usually set a pair of Name Servers to point it to that particular company. On their end, three records are set up automatically as soon as the domain name is added - one A record and two MX records. The first one is a numeric address, or IP address, that “tells” the domain address where its site is, while the other two are alphanumeric and they indicate the server that handles the emails for that particular Internet domain. The website and the e-mail hosting are usually considered to be one thing, while they are in reality two different services. Having independent records for them will allow you to have them with different providers if you want. As an illustration, some new company can have outstanding uptime for your site, but you may not want to switch your emails from your current host and by using an A record to point the Internet domain to the first and MX records to have the emails with the second, you could get the best of both companies. These records are checked when you want to open a website or send an email - in any case, the service provider whose name servers are used for the domain name will 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 email will be delivered.
