Every registered domain has a minimum of two Name Server records which show where it's hosted i.e. by using these records you direct your Internet domain to the servers of a certain web hosting provider. This way, you have both your site and your e-mails managed by the exact same provider. On the lower level of the Domain Name System (DNS), however, there are a number of other records, for instance A and MX. The former shows which server manages the site for a given domain name and is always an IP address (18.104.22.168), while the latter reveals which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, any time you enter a domain address in your Internet browser, your request is directed through the global DNS system to the company whose NS records the domain name uses and from there you will be directed to the servers of a different service provider in case you have set an IP address of the latter as an A record for your domain name. Having different records for the site and the e-mails means that you may have your site and your e-mails with 2 different companies if you'd like.