private static IEnumerable<Type> FindAllMessageHandlers()
{
    var iMessageHandler = typeof(IMessageHandler);
 
    var types = from type in AppDomain.CurrentDomain.GetAssemblies().SelectMany(t => t.GetTypes())
            let canInstantiate = !type.IsInterface && !type.IsAbstract && !type.IsNestedPrivate
            let isIMessageHandler = type.GetInterface(iMessageHandler.Name) != null
            where canInstantiate && isIMessageHandler
            select type;