Fixes: #9825 Issue link: https://github.com/spring-projects/spring-integration/issues/9825 The `DelayerEndpointSpec` extends `ConsumerEndpointSpec` which has a `taskScheduler()` option. However this is set only to the endpoint for this `MessageHandler`. * Override `taskScheduler()` method on the `DelayerEndpointSpec` to set the provided `TaskScheduler` to the `DelayHandler` as well **Auto-cherry-pick to `6.4.x` & `6.3.x`**