Every single registered domain name has a minimum of two Name Server records that show where it's hosted i.e. by using these records you direct your domain address to the servers of a certain web hosting provider. This way, you've got both your website and your emails managed 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, for example A and MX. The former reveals which server manages the website for a given domain and is always an IP address (220.127.116.11), while the latter reveals which server deals with the e-mails and is always an alphanumeric string (mx1.domain.com). For instance, any time you enter a domain address in your browser, your request is forwarded through the global DNS system to the provider whose NS records the domain name uses and from there you will be sent to the servers of a different provider if you have set an IP address of the latter as an A record for your Internet domain. Having different records for the site and the emails means that you can have your website and your emails with 2 different companies if you wish.