Each and every domain which is 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 set up manually if needed. For example, the A record of a domain is its IP address i.e. this record shows where the web site is located; the MX records show where the e-mails are handled, while with an SRV record you can use a domain address for unconventional purposes, such as a Voice-over-IP service. To be able to set up and modify particular records permits you to have different services with different companies if, for example, your current host provides dependable web hosting, but has difficulties with the email service, or you simply prefer to get a certain service from a particular company. While you can set up and modify these records freely and with no restrictions as you own a given domain name, some companies charge extra to give you this option.