OnAfterBind is a TNotifyEvent property that represents the event handler signalled after the socket handle for the client has been bound using the Host and Port for the connection. 

Applications must assign a procedure to the event handler to allow responding to the event notification. 

OnAfterBind is assigned to the event handler of the same name found in the Socket property when an IOHandler is assigned for the client connection. Assigning a new procedure to OnAfterBind will cause the same procedure to be assigned to the event handler in an existing IOHandler. 

Use OnBeforeBind to respond to the event notification that occurs just prior to binding the socket handle for the connection.

TIdTCPClientCustom.OnBeforeBind 

TIdTCPConnection.Socket 

TIdTCPConnection.IOHandler 

TIdIOHanderSocket.OnAfterBind