Any active domain name that's added in a hosting account features a number of records which allow it to work properly. In the common case, the name servers (NS records) show where the domain name 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 such as A (IP address of the website/server), MX (e mail server), SRV (employing a domain address for non-website purposes on a certain port number like Voice-over-IP), etc. Having access to these records and by having the ability to modify them, you may have your web site with company A and your e-mail messages with company B, for example. This offers you more independence since you can choose the best provider for each of these services and you don't have to stick with one company. Whenever you choose a hosting company, you have to make certain that you can access all DNS records freely since some companies have an extra fee for this feature.