Every single registered domain name has at least 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 particular web hosting provider. In this way, you've got both your website and your e-mails managed by the very same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, like A and MX. The former shows which server deals with the website for a given domain address and is always an IP address (188.8.131.52), while the latter shows which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). For example, when you enter a domain in your Internet browser, your request is sent through the global DNS system to the company whose NS records the domain uses and from there you will be forwarded to the servers of a different company provided you have set an IP address of the latter as an A record for your Internet domain. Having separate records for the website and the e-mails means that you could have your website and your emails with 2 different companies if you would like.