Every single registered domain has no less than two Name Server records which show where it is hosted i.e. by using these records you point your domain address to the servers of a specific website hosting company. This way, you've got both your website and your emails managed by the exact same service provider. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, such as A and MX. The former shows which server manages the website for a given domain address and is always an IP address (18.104.22.168), while the second one reveals which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). For example, any time you enter a domain address in your browser, your request is sent through the global DNS system to the provider whose NS records the domain name uses and from there you will 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 separate records for the website and the e-mails means you could have your site and your emails with two different companies if you'd like.