Each registered domain name has a minimum of 2 Name Server records which show where it is hosted i.e. by using these records you point your domain to the servers of a particular web hosting company. In this way, you've got both your site and your e-mails handled by the same company. On the lower level of the Domain Name System (DNS), however, there are lots of other records, such as A and MX. The first one shows which server deals with the site for a given Internet domain and is always an IP address (18.104.22.168), while the latter shows which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, any time you type a domain address in your browser, your request is sent through the global DNS system to the company whose NS records the domain uses and from there you may be sent to the servers of a different provider provided you have set an IP address of the latter as an A record for your Internet domain. Having independent records for the site and the emails means that you can have your website and your e-mails with two different providers if you wish.