Can i RegisterHandler for message queue after start?
I want to set RegisterHandler in Plugin.
No, handlers need to be registered before mqServer.Start() is called.
But you could delay the start of the MQ Server by adding it to AfterInitCallbacks:
AfterInitCallbacks.Add(host => host.TryResolve<IMessageService>().Start());
Or if you want to wrap this in a plugin you can add it inside and IPostInitPlugin Plugin Interface which is called after all plugins are registered.