Every registered domain has no less than two Name Server records which show where it's hosted i.e. by using these records you point your domain to the servers of a particular web hosting company. This way, you've got both your site and your emails managed by the same company. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, for example A and MX. The first one shows which server deals with the site for a given Internet domain and is always an IP address (123.123.123.123), while the second one reveals which server handles the e-mails and is always an alphanumeric string (mx1.domain.com). As an example, when you type a domain address in your 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 another 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 can have your website and your e-mails with 2 different providers if you would like.