Then register under https://lobby.siedler3.net or after starting the aLobby with your nickname and your email address. You will then receive the VPN key that was already assigned to you.
Hints:
Your nickname is also registered in the forums with exactly the same email address.
After you have registered in the aLobby, you have to wait max. 1 hour until the VPN key is assigned to your aLobby-account by the system. You just have to restart the aLobby then to get the key.