A. In Microsoft Exchange Server, if you don't have Deleted item retention turned on for the public Information Store (IS), you can't recover items you delete from a public folder after you delete them. To enable Deleted item retention on a public IS, select the public IS of your choice in Exchange Administrator, and open the Properties dialog box. Change the Deleted item retention time (days) to whatever non-zero value you want to use. Once you've done so, you'll be able to recover deleted items from that point forward.
When someone deletes an item from a public folder, the retention process works differently from the way it works for mailboxes. Instead of using a special Deleted items folder, as the private IS does, the public IS marks deleted items as deleted and hidden. To recover an item, you still right-click its parent folder to get the Recover deleted items command, but you must have Editor (or equivalent) permissions on the folder. In addition, you must have Item recovery turned on for the public IS of the server that hosts the public folder replica you're using—it's not enough just to turn on Retention on one of the replica servers.