Each registered domain name has no less than 2 Name Server records which show where it's hosted i.e. by using these records you point your domain to the servers of a specific hosting provider. In this way, you have got both your site and your emails handled by the exact same company. On the lower level of the Domain Name System (DNS), on the other hand, there is a variety of other records, like A and MX. The first one shows which server manages the site for a given domain name and is always an IP address (123.123.123.123), while the latter reveals which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). For example, whenever you type a domain in your Internet browser, your request is forwarded through the global DNS system to the company whose NS records the domain address uses and from there you may be directed to the servers of another service provider provided you have set an IP address of the latter as an A record for your domain name. Having independent records for the site and the emails means that you may have your website and your emails with 2 different companies if you wish.
