To merge folders of emails from multiple Outlook accounts.
Open the account to merge from in Outlook. Drag the folder(s) to be merged to the desktop. Should create ".mbox" files. Log into the account to merge into using Mail (version with OS X 10.10 works well). Use Import Mailboxes, Files in mbox format, choose the files. Copy the imported mailboxes onto the server account. That account (with the new folders) will now be accessible from Outlook.
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