Every registered domain has at least two Name Server records that show where it is hosted i.e. by using these records you point your domain name to the servers of a certain web hosting provider. In this way, you have both your website and your emails managed by the same provider. On the lower level of the Domain Name System (DNS), on the other hand, there are a number of other records, like A and MX. The former shows which server handles the website for a given domain address and is always an IP address (184.108.40.206), while the latter shows which server deals with the emails and is always an alphanumeric string (mx1.domain.com). For instance, when you type a domain name in your browser, your request is directed through the global DNS system to the provider whose NS records the domain address uses and from there you will be forwarded to the servers of a different service provider provided you have set an IP address of the latter as an A record for your domain address. Having independent records for the site and the emails suggests that you can have your site and your e-mails with two different providers if you would like.