Every domain name which is registered and hosted has a great deal of DNS records - some of them are created automatically when you host a domain, others can be set up manually if required. As an example, the A record of a domain address is its IP address i.e. this record shows where the web site is situated; the MX records reveal where the e-mails are handled, 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 enables you to have different services with different providers if, for instance, your current host provides stable web hosting, but has troubles with the e-mail service, or you simply prefer to get a particular service from a particular company. Although you should be able to set up and edit these records freely and without any limits as you own a given domain name, a lot of companies charge extra to give you this option.