Every single registered domain has no less than 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 particular hosting company. This 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), nevertheless, there is a variety of other records, like A and MX. The former reveals which server deals with the website for a given domain and is always an IP address (220.127.116.11), while the second one shows which server manages the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, when you enter a domain name in your browser, your request is forwarded through the global DNS system to the company whose NS records the domain name 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 Internet domain. Having separate records for the website and the emails means you may have your site and your emails with 2 different providers if you wish.