Every single registered domain name has at least 2 Name Server records which show where it is hosted i.e. by using these records you direct your domain address to the servers of a specific hosting company. That way, you have both your site and your e-mails managed by the exact same company. On the lower level of the Domain Name System (DNS), however, there is a variety of other records, for example A and MX. The first one shows which server deals with the site for a given domain address and is always an IP address (18.104.22.168), while the second one reveals which server handles the e-mails and is always an alphanumeric string (mx1.domain.com). For example, when you type a domain in your browser, your request is sent through the global DNS system to the provider whose NS records the domain uses and from there you will be forwarded to the servers of a different provider in case you have set an IP address of the latter as an A record for your domain address. Having independent records for the website and the emails suggests that you may have your site and your emails with two different providers if you would like.