Each registered domain has at least 2 Name Server records that show where it is hosted i.e. by using these records you point your Internet domain to the servers of a specific web hosting provider. That way, you have got both your site and your emails managed by the exact same provider. On the lower level of the Domain Name System (DNS), nevertheless, there are lots of other records, such as A and MX. The former shows which server deals with the website for a given domain and is always an IP address (123.123.123.123), while the latter indicates which server handles the e-mails and is always an alphanumeric string (mx1.domain.com). For example, when you type a domain name in your browser, your request is forwarded through the global DNS system to the company whose NS records the domain uses and from there you will be forwarded to the servers of another provider in case you have set an IP address of the latter as an A record for your domain address. Having different records for the website and the e-mails suggests that you can have your website and your emails with two different companies if you would like.