These states provide information about current user's activities on your Pop3 server. When user connects to server, appropriate events are fired and state is set to 'StateConnecting' until he provides username/password combination. Once user provides this information and logs on, 'StateLoggedIn' is set and will remain so until disconnection.

Specially, during user's retrieval of the message 'StateSendingMessage' is set and in that time you should not expect to receive any commands from the user.