This article goes over Exchange Online Archive Requirements and the headache of licensing for it. I recently completed a staged migration from exchange 2007 to exchange online. If you have any users over 50 GB you need the exchange online archive.
Upload all your archive files using Azure copy (see https://docs.microsoft.com/en-us/office365/securitycompliance/use-network-upload-to-import-pst-files for instructions). Afterward, make sure to check https://outlook.office365.com/owa/ to verify the archive emails. You may notice that their outlook doesn’t show the archive. Well, you need the correct outlook license! I found the following article about Licenses and Exchange Online Archiving.
Which Outlook to use?
In short, If you don’t have Pro Plus, Stand-Alone Outlook, or Office E3+ plan you CAN NOT use the exchange online archive in outlook. Buy the appropriate license and then reinstall the office for that user. Its a pain, but needed for the archive to function properly. Personally, I just went ahead and bought the Pro Plus and installed it for that user since we only have one user needing it.
In my opinion, this was a horrible licensing decision by Microsoft and they should revert it so any outlook can access it. In closing, the exchange online archive requires are a bit crazy, you need both the exchange archive plan and an outlook version that supports it. This couldn’t be any more confusing as Microsoft licensing usually is.
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