If you are a publisher, you will see the pending and scheduled messages in a list at the top along with recent messages. When you will click a pending message, you will have the ability to Publish or Reject the message. Click on the Reject button to reject the message. You will have to provide a reason for rejecting the message. The reason will be sent to the author informing him/her that the message has been rejected.
An email notification will be sent to author to notify that message has been rejected.
As an author, you will be able to see the reason of rejection.