Every registered domain has at least 2 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 specific website hosting company. This way, you have both your site and your emails handled by the same provider. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, like A and MX. The former reveals which server handles the site for a given domain and is always an IP address (126.96.36.199), while the second one reveals which server manages the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, whenever you type a domain 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 could be sent to the servers of another provider if you have set an IP address of the latter as an A record for your domain. Having independent records for the website and the e-mails means that you may have your site and your e-mails with two different companies if you'd like.