ListenQueue is an Integer property that indicates the maximum number of unresolved connection attempts allowed for each listener thread. When a listener thread has more pending connection requests than the value in ListenQueue, the MaxConnectionReply response is sent to the client and the new connection is closed. 

The default value for ListenQueue is IdListenQueueDefault as assigned during initialization of the component. ListenQueue is used as an argument when socket descriptors for listener threads are created during server activation. Any change to the value in ListenQueue must be made prior to setting Active to True. 

On the Windows platform, the default listen queue size can be determined by the Operating System. 

Non-server versions of Windows 95, Windows NT, Windows 2000, and Windows XP are internally limited to a maximum of 5 queued connection requests per listening socket. Server versions of Windows NT, Windows 2000, and Windows XP are internally limited to a maximum of 200 queued connection requests per listening socket. 

Setting ListenQueue to a larger value will not override any internal limitation of the Operating System.

TIdListenerThread 

IdListenQueueDefault 

MaxConnections 

MaxConnectionReply 

Active