When you add a domain name as hosted in some account, you typically set a pair of Name Servers to point it to that specific service provider. On their end, 3 records are set up automatically as soon as the domain is added - one A record and two MX records. The former is a numeric address, or IP address, that “tells” the Internet domain where its website is, while the other two are alphanumeric and they indicate the server that deals with the emails for that specific Internet domain. The website and the email hosting are generally perceived as one thing, while they are actually two different services. Having different records for them will permit you to have them with different companies if you'd like. As an example, some new company can have superb uptime for your site, but you might 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 emails with the latter, you could get the best of both companies. These records are checked when you wish to open a website or send an e-mail - in either case, the company 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'll see the needed site or your email is going to be delivered.