Each registered domain name has no less than two Name Server records which show where it's hosted i.e. by using these records you direct your domain to the servers of a particular web hosting company. In this way, you have both your website and your emails handled by the very same provider. On the lower level of the Domain Name System (DNS), nevertheless, there is a variety of other records, such as A and MX. The first one reveals which server deals with the website for a given domain name and is always an IP address (123.123.123.123), while the second one reveals which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). As an example, when you type a domain name in your browser, your request is sent through the global DNS system to the provider whose NS records the domain uses and from there you could be directed to the servers of a different provider in case you have set an IP address of the latter as an A record for your domain address. Having separate records for the website and the e-mails means that you can have your website and your emails with two different companies if you wish.