NoRouteToHostException

I have a program(java application)which sends mails to multiple addresses through a mailserver host(i tried using many mail servers.all valid ipaddresses).My machine is behind a proxy server.I keep getting a NoRouteToHostException.Can anybody update me on this.I'm not using javamail.
it's urgent.

Pretty simple, you can either get there or you cannot. In your case you cannot. Sometimes, proxies disallow certain protocols or filter specific addresses. Or perhaps a outbound router is not doing it's job. You'll need to contact you network guys, or run a LLC trace.