Each and every domain name that is registered and hosted has a lot of DNS records - some of them are set up automatically when you host a domain, others can be created by hand if needed. For instance, 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 show where the emails are managed, while with an SRV record you can use a domain address for unconventional purposes, for instance a Voice-over-IP service. The ability to set up and modify particular records permits you to have different services with different companies if, for instance, your present host provides stable web hosting, but has difficulties with the e-mail service, or you simply prefer to get a specific service from a certain company. Even though you can create and modify these records freely and with no restrictions as you own a given domain address, a lot of companies charge extra to give you this option.