When you add a domain name as hosted in some account, you typically set a pair of Name Servers to direct it to that particular company. On their end, three records are set up automatically the moment the domain name is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the domain address where its website is, while the other two are alphanumeric and they show the server that deals with the e-mails for that particular Internet domain. The website and the email hosting are usually regarded as one thing, when they're in reality two different services. Having separate records for them will permit you to have them with different companies if you want. For instance, some new company may have excellent uptime for your website, 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 first and MX records to have the e-mails with the second, you will 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 will be contacted to retrieve the A and MX records and if you've set records different from their own, the correct web/mail server will then be contacted and you are going to see the needed site or your e-mail is going to be delivered.