Every single registered domain has at least 2 Name Server records that show where it's hosted i.e. by using these records you point your Internet domain to the servers of a certain website hosting provider. In this way, you have got both your site and your e-mails managed by the same company. On the lower level of the Domain Name System (DNS), on the other hand, there are a number of other records, for example A and MX. The former shows which server handles the site for a given Internet domain and is always an IP address (126.96.36.199), while the second one indicates which server handles the emails and is always an alphanumeric string (mx1.domain.com). For example, when you type a domain name in your Internet browser, your request is sent through the global DNS system to the provider whose NS records the domain address uses and from there you could be sent to the servers of another company provided you have set an IP address of the latter as an A record for your domain name. Having separate records for the site and the emails means that you may have your website and your emails with two different companies if you wish.