Symptom: At you new site you have set up your email server and you can send but can't receive email. Similarly all your ports may be open and yet you still can't connect form outside the lan. This may also be the case for other types of connection such as VoIP .

 Why can't you connect?

We will use both ping and telnet to test the connection and narrow down where the block lies.

1. Firstly test that you can connect to the router by pinging the wan ip from outside the lan. Make it easier on yourself by using vnc or rdp to take control of the remote computer to perform this test.
2. Secondly forward data arriving at port 25 to the lan ip address of the server.
3. Now telnet to the wan ip but specifying that you want to connect through port 25 by typing the following at the command line where the x's are replaced by the ip address or host name; telnet xxx.xxx.xxx.xxx 25. You can test any port in this manner. eg telnet xxx.xxx.xxx.xxx 3389 to test whether rdp port 3389 is open.
4. eg typing telnet www.solvedit.com.au 25 at the command line will clear the command line window and replace it with a telnet window waiting for input.Type quit to exit out of telnet.
   
5. If the connection doesn't work then you know that you are unable to connect to that port from the wan. Now try connecting to the port from the lan. eg if the server's lan ip is 192.168.0.1 then type telnet 192.168.0.1 25 on the command line from a computer on the lan. If you can connect on the lan but not the wan then we can say that the server service is working.
6. If the server service is working, you can connect from the lan but not the wan then the blockage m