Whether or not you need port forwarding is dependent on how your router's firewall is set. I have a dsl modem/router so I will talk about this. Other routers will have similar settings but I cannot generalize about the exact settings. Most router's firewall is set to minimum. This means the firewall will block all incoming attempts to access your network. The next level on the firewall will block all outgoing attempts unless the ports can be opened. This is where port forwarding comes in.
So if the firewall on the minimum setting blocks all incoming attempts, how does something like a voip adapter get through? The voip adapter initiates access to the server from your network. Once this happens, there is a port open for the voip server to access the adapter.
If the firewall is set to a higher level, then you must tell the firewall which port to open for a given device. I doubt your firewall is set above minimum so you shouldn't need port forwarding. If your email software works, then I would say the firewall is definitely at minimum.