Any active domain that is added in a hosting account includes a variety of records which allow it to work properly. In the common case, the name servers (NS records) show the location where the Internet domain is hosted and they are set on the side of the registrar company, but on the lower level there are particular records set through the hosting company like A (IP address of the website/server), MX (email server), SRV (employing a domain name for non-website purposes on a specific port number such as Voice-over-IP), etc. Having access to these records and by having the capacity to modify them, you can have your website with company A and your e-mail messages with company B, for example. This gives you more flexibility because you can pick the best provider for every one of these services and you do not have to stick with only one company. Whenever you pick a hosting company, you have to make certain that you have access to all DNS records freely since some providers have an additional fee for this feature.