Each and every domain which is registered and hosted has lots of DNS records - some of them are created automatically when you host a domain, others can be created manually if required. As an illustration, 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 e-mails are stored, while with an SRV record you can use a domain for unconventional purposes, for instance a Voice-over-IP service. Being able to set up and modify particular records enables you to have different services with different companies if, for instance, your current host provides good web hosting, but has problems with the email service, or you simply prefer to get a particular service from a certain company. While you can create and modify these records freely and with no restrictions as you own a given domain address, many companies charge extra to give you this option.