Every domain that's registered and hosted has quite a lot of DNS records - some of them are set up automatically when you host a domain, others can be created manually if required. As an illustration, the A record of a domain name is its IP address i.e. this record reveals where the site is located; the MX records show where the emails are stored, while through an SRV record you can use a domain for unconventional purposes, like a Voice-over-IP service. The ability to create and modify certain records permits you to have different services with different companies if, for instance, your current host provides good web hosting, but has problems with the email service, or you simply prefer to get a particular service from a specific company. Though you must be able to set up and modify these records freely and with no limitations as you own a given domain address, lots of companies charge extra to give you this option.