Mailboxes need to be visible in order to be enabled within EV.

There may be some registry keys that can help you.  You might want to lodge a support case and see if they can help.

Ben

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You can execute the following SQL statement which will enable EV to see the hidden mailboxes:

USE EnterpriseVaultDirectory

UPDATE ExchangeMailboxEntry

SET MbxExchangeState = '0' WHERE MbxExchangeState = '2'

Once you run that, close and reopen the admin console - you should then be able to see the hidden mailboxes and enable them.  They will revert back to being hidden, but I'm not sure what the timeout is.

Does this allow EV to archive hidden maiboxes?  I was under the impression that was not possible..

Haven't confirmed with what was in the mailbox itself but it did allow me to then migrate some old pst's into the mailbox

So Thanks it helped us out