Every registered domain name has at least 2 Name Server records that show where it's hosted i.e. by using these records you direct your domain to the servers of a particular hosting provider. This way, you've got both your site and your emails handled by the same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, for instance A and MX. The former reveals which server handles the website for a given Internet domain and is always an IP address (188.8.131.52), while the latter reveals which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an example, when you type a domain name in your browser, your request is sent through the global DNS system to the company whose NS records the domain address uses and from there you may be directed to the servers of a different company provided you have set an IP address of the latter as an A record for your domain address. Having independent records for the website and the emails means you can have your website and your emails with two different providers if you would like.