Every single registered domain name has a minimum of 2 Name Server records that show where it's hosted i.e. by using these records you point your domain to the servers of a particular web hosting provider. This way, you have got both your website and your e-mails handled by the very same service provider. On the lower level of the Domain Name System (DNS), nevertheless, there are a number of other records, such as A and MX. The first one shows which server manages the website for a given Internet domain and is always an IP address (123.123.123.123), while the second one reveals which server handles the emails and is always an alphanumeric string (mx1.domain.com). For example, when you enter a domain name in your browser, your request is forwarded through the global DNS system to the provider whose NS records the domain address uses and from there you could be sent to the servers of another 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 emails means you can have your site and your e-mails with two different providers if you'd like.