Every single registered domain has a minimum of two Name Server records that show where it's hosted i.e. by using these records you point your domain name to the servers of a specific hosting company. This way, you have got both your website and your e-mails managed by the very same provider. On the lower level of the Domain Name System (DNS), however, there is a variety of other records, for example A and MX. The former reveals which server handles the site for a given domain address and is always an IP address (188.8.131.52), while the second one shows which server deals with the emails and is always an alphanumeric string (mx1.domain.com). As an example, any time you enter a domain in your web browser, your request is forwarded through the global DNS system to the provider whose NS records the domain uses and from there you may be directed to the servers of a different company in case you have set an IP address of the latter as an A record for your domain. Having independent records for the website and the e-mails suggests that you may have your site and your emails with two different providers if you wish.