Each domain name that is registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be set up by hand if required. For example, the A record of a domain is its IP address i.e. this record reveals where the site is located; the MX records show where the e-mails are managed, while with an SRV record you can use a domain address for unconventional purposes, such as a Voice-over-IP service. The ability to create and modify certain records allows you to have different services with different companies if, for illustration, your current host provides good web hosting, but has issues with the e-mail service, or you simply prefer to get a specific service from a particular company. Though you can set up and edit these records freely and with no restrictions as you own a given domain address, lots of companies charge extra to give you this option.