Each registered domain has at least two Name Server records that show where it's hosted i.e. by using these records you point your domain address to the servers of a particular web hosting company. This way, you have both your website and your e-mails handled by the exact same service provider. On the lower level of the Domain Name System (DNS), on the other hand, there is a variety of other records, such as A and MX. The first one reveals which server manages the site for a given domain name and is always an IP address (184.108.40.206), while the latter reveals which server manages the emails and is always an alphanumeric string (mx1.domain.com). As an example, whenever you enter a domain name in your Internet browser, your request is forwarded through the global DNS system to the provider whose NS records the domain address uses and from there you could be forwarded to the servers of a different provider if you have set an IP address of the latter as an A record for your domain. Having independent records for the site and the emails means that you may have your website and your emails with two different providers if you wish.