Every single registered domain name has at least two 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 web hosting company. This way, you have got both your site 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 example A and MX. The first one shows which server manages the website for a given domain name 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). As an example, any time you enter a domain address in your web browser, your request is forwarded 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 another company if you have set an IP address of the latter as an A record for your domain address. Having different records for the website and the emails means that you can have your site and your e-mails with 2 different companies if you'd like.