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 set up automatically when the domain name is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the domain name where its site is, while the other two are alphanumeric and they indicate the server that handles the e-mails for that specific domain name. The website and the e-mail hosting are usually regarded as one thing, while they're in fact two different services. Having separate records for them will permit you to have them with different providers if you wish. As an illustration, some new provider might have outstanding uptime for your website, but you may not want to switch your e-mail messages from your current host and by employing an A record to point the domain to the first and MX records to have the e-mails with the latter, you could get the best of both companies. These records are checked when you want to open a website or send an e-mail - either way, the company whose name servers are used for the domain address 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're going to see the needed website or your e-mail is going to be delivered.
