Each registered domain has a minimum of two Name Server records which show where it is hosted i.e. by using these records you direct your domain to the servers of a specific website hosting company. In this way, you've got both your website and your emails managed by the exact same company. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, for instance A and MX. The first one shows which server handles the website for a given domain and is always an IP address (18.104.22.168), while the second one shows which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, any time you enter a domain address in your Internet browser, your request is directed through the global DNS system to the company whose NS records the domain name uses and from there you may be sent 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 different records for the site and the emails means you could have your site and your e-mails with two different companies if you wish.