Postings to Moderated folders must be reviewed by that folder's moderator and approved for posting before they appear in the folder.
Unmoderated folders are wide open for anyone to use, and postings appear immediately.
When you create a message post and send it, the Exchange server checks your permission settings for that particular public folder. If you have moderator level permission for that public folder then the message will be posted. Please note that submissions to some folders or discussion groups are reviewed to determine whether they should be made publicly available. In these cases, there will be a delay before approved submissions can be viewed by others. Once the message post is reviewed and approved by a moderator the message will be posted to the public folder.