Whenever you add a domain as hosted in some account, you typically set a pair of Name Servers to direct it to that particular company. On their end, 3 records are created automatically right after the Internet domain is added - one A record and two MX records. The first one is a numeric address, or IP address, which “tells” the domain address where its site is, while the other two are alphanumeric and they reveal the server that handles the emails for that specific Internet domain. The site and the e-mail hosting are usually considered to be one thing, while they're in fact two different services. Having different records for them will enable you to have them with different providers if you would like. As an illustration, some new company may have outstanding uptime for your site, but you may not want to switch your e-mails from your current host and by using an A record to point the domain name to the former and MX records to have the e-mails with the second, you can get the best of both companies. These records are checked when you want to open a website or send an email - either way, 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've set records different from their own, the right web/mail server will then be contacted and you are going to see the needed website or your e-mail is going to be delivered.