Enable an archive for existing mailbox
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You can create archives for existing users that have a mailbox but aren’t archive-enabled. This is known as enabling an archive for an existing mailbox.
Use the EAC
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1. Navigate to Recipients > Mailboxes.
2. Select a mailbox.
3. In the details pane, under In-Place Archive, click Enable.
tipTip:
You can also bulk-enable archives by selecting multiple mailboxes (use the Shift or Ctrl keys). After selecting multiple mailboxes, in the details pane, click More options. Then, under Archive click Enable.