Each registered domain name has no less than two Name Server records that show where it's hosted i.e. by using these records you point your domain to the servers of a specific hosting company. In this way, you have both your site and your emails managed by the same provider. On the lower level of the Domain Name System (DNS), however, there is a variety of other records, for instance A and MX. The first one reveals which server manages the site for a given Internet domain and is always an IP address (188.8.131.52), while the second one indicates which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). For example, any time you enter a domain address in your browser, your request is forwarded through the global DNS system to the company whose NS records the domain address uses and from there you will be directed to the servers of another provider provided you have set an IP address of the latter as an A record for your domain address. Having separate records for the site and the e-mails means you may have your site and your emails with 2 different companies if you would like.