Every registered domain name has a minimum of two Name Server records which show where it is hosted i.e. by using these records you point your domain to the servers of a certain website hosting provider. This way, you have got both your site and your e-mails handled by the same company. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, like A and MX. The first one shows which server deals with the website for a given domain name and is always an IP address (18.104.22.168), while the second one indicates which server deals with the emails and is always an alphanumeric string (mx1.domain.com). For instance, when you type a domain address in your Internet browser, your request is sent through the global DNS system to the company whose NS records the domain uses and from there you could be forwarded to the servers of another company provided you have set an IP address of the latter as an A record for your domain name. Having independent records for the site and the emails means that you can have your site and your e-mails with two different companies if you wish.