Each registered domain has no less than two Name Server records which show where it's hosted i.e. by using these records you direct your domain name to the servers of a particular web hosting provider. This way, you have got both your site and your emails handled by the exact same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, for example A and MX. The former shows which server manages the website for a given domain address and is always an IP address (123.123.123.123), while the second one indicates which server handles the emails and is always an alphanumeric string (mx1.domain.com). As an illustration, when you type a domain 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 could be forwarded to the servers of another company provided you have set an IP address of the latter as an A record for your Internet domain. Having independent records for the site and the emails means you may have your website and your e-mails with two different providers if you wish.