Whenever you add a domain as hosted in some account, you normally set a pair of Name Servers to direct it to that specific company. On their end, 3 records are created automatically when the Internet domain is added - one A record and two MX records. The former 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 e-mails for that particular Internet domain. The site and the e-mail hosting are usually regarded as one thing, when they're actually two different services. Having separate records for them will enable you to have them with different providers if you want. For example, some new company can have fantastic 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 Internet domain 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 whenever you want to open a site or send an email - in either case, the provider 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 email will be delivered.