Each 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 to the servers of a specific website hosting provider. This way, you have got both your website and your emails handled by the same service provider. On the lower level of the Domain Name System (DNS), however, there are lots of other records, for example A and MX. The first one shows which server manages the site for a given domain name and is always an IP address (184.108.40.206), while the second one indicates which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you type a domain in your Internet browser, your request is directed through the global DNS system to the company whose NS records the domain address uses and from there you will be forwarded to the servers of a different service provider if 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 may have your website and your e-mails with 2 different providers if you'd like.