The easiest method of getting this information is by contacting your ISP and asking them. However, if this isn't preferred then you can attempt to extract the information from your computer.
First it depends on how your network is set up at home. If you are using ICS or a proxy to share the Internet connection amongst multiple computers, and Ability Mail Server is located on another computer without direct access to the Internet, then you need to retrieve the information from the computer which is sharing the Internet connection. If Ability Mail Server is running directly on the computer with the Internet connection, then you are fine to get the information from that computer directly. The method of retrieving the DNS information depends on your operating system...
Windows 95, 98, Me...
1. Open an MS-DOS prompt.
2. Type "winipcfg" and hit the ENTER key.
3. On the dialog that appears, select the correct network device from the drop down list.
4. You should now see details of your computers Internet connection, one or two of which should be the DNS servers
Windows NT, 2000, XP and 2003...
1. Open a Command Console (Run: cmd).
2. Type "ipconfig/all" and hit the ENTER key.
3. Scroll up or down the list of network devices and locate your Internet network device.
4. You should be able to view the 'DNS Servers'. The IPs listed here are your Internet provider's DNS servers.