You can use the Microsoft Exchange Server Public Folder DAV-based Administration (PFDAVAdmin) tool to recover public folders or items. You can use the following methods when you cannot recover folders or items by using the Recover deleted items command in Microsoft Outlook. PFDAVAdmin is supported when running with Exchange 2000 Server, Exchange Server 2003 and Exchange Server 2007.

Note Deleted folders or items are preserved only if the Keep deleted items for (days) option is enabled on the public store.

Recover a deleted public folder

1. Move to the PFDAVAdmin folder, and then double-click the PFDAVAdmin.exe file.
2. On the File menu, click Connect.
3. In the Exchange server box, type the name of the Exchange server to which you want to connect.
4. In the Global Catalog box, type the name of the global catalog server.
5. If it is required, click to clear the Authenticate as currently logged-on user check box. Type an appropriate user name, password, and domain in the respective boxes.
6. In the Connection area, click Public Folders, and then click OK.
7. Expand Public Folders, and then click the parent folder of the deleted folder.
8. Right-click the parent folder, and

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If you are facing the task of demoting your domain controller running exchange, because you either have a new dc added to your network and want to move some roles over to that brand new sparkling server.
Then you cannot do a dcpromo /demote on the exchange server! This will cause havoc.

What you must do is: Add another Exchange server to your network move the mailboxes over and deinstall exchange on the DC. Then do a dcpromo /demote reinstall exchange move mailboxes over again.
This is the way with the shortest downtime