You can also look to a third-party tool to handle the export, rehydration, and upload process but you want to make sure the tool is solid.
Either way, legacy archive export is hairy business.
Office 365 gotcha No. 6: Grinding to a halt during data import
Exporting legacy data is half the battle. Ingesting this data into Office 365 presents a range of problems, one of which is that Exchange Web Services (EWS) hits a wall at 400GB per day, with a 250MB- to 500MB-per-hour typical ingestion speed. If you're looking at large amounts of data, on the order of multiple terabytes, it's going to take a long time.
But the bottleneck might not be EWS; your Internet bandwidth could just as easily slow you down. Depending on the data volumes you are ingesting, it can grind to a near halt. There are several third-party solutions to consider for assisting in this regard, or you might think about moving your archive data from an on-premises solution to a cloud-based solution other than Microsoft.
Office 365 gotcha No. 7: Failing to know the limitations of Exchange Online
Message retrieval is a common pain point for admins. With Office 365, that pain can be unbearable, as Office 365 doesn't perform message retrieval beyond the deleted item retention limit, which is 14 days by default.
There's an easy solution: Alter your deleted item retention limit. Of course, it's a little trickier with Office 365. As opposed to on-premises Exchange, where you can touch the servers directly and alter the retention time, Office 365 requires a remote PowerShell connection to make the change. Here's the bad news: The max retention limit is 30 days. That's it!
There are two ways around this gotcha. You can put mailboxes on Litigation Hold, in which case you may look to add the archive add-on piece for limitless hold, or you can implement an archive solution that works with Office 365 so that messages are retained and easily recovered.
Office 365 gotcha No. 8: Failing to factor in the cost of à la carte add-ons
If you think Office 365 is an all-you-can-eat buffet, you are right — to a degree. Many features you might expect from the online suite are built in. But to include certain features, you will have to spend a bit more money to get the service you want.
Be sure to thoroughly vet your plan's offerings and research the "purchase services" option through your Office 365 dashboard to determine whether any of the paid services will be required for your organizational needs. Some examples include Visio Pro for Office 365, Project Pro for Office 365, Yammer Enterprise, and the like.
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