Each registered domain has no less than two Name Server records which show where it's hosted i.e. by using these records you point your domain to the servers of a certain website hosting provider. In this way, you've got both your site and your emails managed by the exact same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, such as A and MX. The former shows which server manages the website for a given domain name and is always an IP address (188.8.131.52), while the latter indicates which server manages the emails and is always an alphanumeric string (mx1.domain.com). For instance, whenever you type a domain address in your browser, your request is directed through the global DNS system to the company whose NS records the domain uses and from there you may be sent to the servers of a different company in case you have set an IP address of the latter as an A record for your Internet domain. Having different records for the website and the emails means that you may have your website and your e-mails with two different providers if you would like.