Exchange 2010: Remove Administrator Mailbox

I know this is an old question, but to convert public folders to a mailbox, you would simply click on All Folders in Outlook, click the top-level public folder and then export that folder to a PST, ensuring you have checked to include all subfolders.

Then once exported you would import into the shared mailbox you have set up.

I understand the need for this policy change as Office 365 and Exchange 2013 do not support public folders (AFAIK). A shared mailbox is the accepted alternate solution, and in many ways works better than public folders (it is already mail-enabled, for one, you can set up inbound rules, for two, and auto-organization should you ever want to send inbound faxes to a specific folder of said mailboxes using inbound mail rules).

Offline defrags? Is it 2005?

Create a new database and move the mailboxes. Zero risk, zero downtime - unlike an offline defrag.

If you really don't have the space, then another option would be to stand up a temporary Exchange server, move those mailboxes you want to delete to that temporary server and delete them from there. That should give the white space back to the database much quicker than anything else.

Finally, there is another technique to remove those mailboxes using remove-storemailbox. It is outlined in this blog posting:

http://blog.enowsoftware.com/solutions-engine/bid/131820/Moving-Exchange-2010-Mailboxes-to-Create-White-Space