# dig +short test.openresolver.com TXT @1.1.1.1 (IP of the server)

Other Information

Test your server for an open DNS resolver here:

http://openresolver.com/

Closing DNS Resolvers on Windows Server 2003/2008/2008 R2:

http://technet.microsoft.com/en-us/library/cc787602(v=ws.10).aspx

Windows Servers running Plesk:

http://kb.parallels.com/en/116463

Closing DNS Resolvers on Servers running Bind:

http://www.zytrax.com/books/dns/ch9/close.html