I found a kb article that may help:

esg70860

Symptom: Extract returns errors: Skipping (NonUser Mailbox)

Cause: The login account used to run EmailXtract does not have permissions to modify items on the Exchange server.

Fix: Verify that the login account used to run the Extract task has adequate permissions to access the mailboxes being archived.

I had worked on a ticket with this same issue the other day...


We resolved the issue by removing "cache mode" from the journaling mailbox on the Extender Server.

Control Panel > Mail > Email Accounts > View or change existing e-mail accounts > change > deselect Use Cached Exchange Mode checkbox.

Attempt to run an extract task.

If this doesn't resolve your issue, I would ensure that the accounts are not disabled in AD, and then continue with Frank's recomendation.

Hope this helps.