Each and every domain name that's registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be created manually if required. For instance, the A record of a domain address is its IP address i.e. this record reveals where the site is situated; the MX records show where the emails are handled, while with an SRV record you can use a domain for unconventional purposes, including a Voice-over-IP service. The ability to set up and modify specific records permits you to have different services with different companies if, for instance, your current host provides stable web hosting, but has issues with the email service, or you simply prefer to get a specific service from a specific company. Even though you must be able to set up and edit these records freely and without any limitations as you own a given domain name, lots of companies charge extra to give you this option.