Each 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 Internet domain to the servers of a specific hosting company. This way, you've got both your site and your e-mails managed 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 former shows which server manages the website for a given Internet domain and is always an IP address (18.104.22.168), while the latter shows which server deals with the e-mails 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 directed through the global DNS system to the company whose NS records the domain uses and from there you may be directed to the servers of a different company in case you have set an IP address of the latter as an A record for your domain. Having different records for the site and the e-mails means you could have your website and your e-mails with two different providers if you'd like.