When you add a domain name as hosted in some account, you usually set a pair of Name Servers to point it to that specific company. On their end, 3 records are created automatically when the domain address 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 website is, while the other two are alphanumeric and they indicate the server that handles the emails for that specific Internet domain. The site and the email hosting are often considered to be one thing, while they're actually two different services. Having independent records for them will enable you to have them with different companies if you want. As an example, 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 using an A record to point the domain to the first and MX records to have the e-mails with the second, you could get the best of both providers. These records are checked when you wish to open a site or send an email - in either case, the provider whose name servers are used for the domain will be contacted to retrieve the A and MX records and if you have set records different from their own, the right web/mail server will then be contacted and you'll see the needed site or your email is going to be delivered.