Some backstory: In the “old” days, mail systems didn’t have 50 GB mailboxes like in Office 365 (I know it’s hard to believe, but trust me). Mailboxes were small because the storage of mailboxes was expensive. Saving and retrieving data had to be fast, and equally so the storage, requiring high-RPM disks. That meant that you had to invest in more expensive storage. Increasing a mailbox size had the downside of a much higher price in storage costs.
To allow people to grow their mailboxes and make sure that companies didn’t go bankrupt due to the storage costs, systems like Enterprise Vault were invented. They would allow you to store regular emails on slow, cheaper storage while maintaining a shortcut to the archived emails in your active mailbox.
Those shortcuts are called stubs. The stub would still have all the necessary information like receiver, sender, and read status, but would be stripped of the message body and attachments.
If you wanted to see the full body and attachments, you could use a plugin—or in later versions, you would double-click on the stub and the archive system would give you back the full message on the fly.
Fast forward to today: A lot of companies with a system like Enterprise Vault are thinking about moving to Office 365. Something often overlooked when migrating mailboxes is handling the stubs. It doesn’t matter what migration system you use; you need to know how to manage the stubs. Microsoft Hybrid will migrate the stub but may not generate the full message (depending on how your Enterprise Vault is set up). Microsoft Hybrid has no way of injecting the migrated data back into the stub.
Joining the archived body, attachments, and the stubs as a full message again is called Stub Rehydration. Microsoft doesn’t currently have a solution to deal with this. Most third-party migration tools that focus on mailbox migrations don’t know what to do with stubs. They may see stubs as a regular message and during the migration, some critical metadata is stripped, preventing stub rehydration. Choose your tool wisely; Microsoft Hybrid and MigrationWiz by BitTitan are “stub-aware” solutions and do not strip that data. (These are the only two I have tested and can vouch for.)
How do I continue from here where I have stubs? You need a provider with the tools to rehydrate stubs. As far as I know, BitTitan is the only partner that provides you with a full service—through Archive Migration Service—relieving you of the need for expertise on top of the pain of running a complex tool.
BitTitan connects active mailbox migration with archive migration with Inflight Stub Rehydration. This means that when a stub is detected during the active mailbox migrations, a call is sent to retrieve the necessary data like body and attachments. That data is combined with the stub and the full message is written in the destination mailbox, removing any delays in the stub rehydration process.
Check out our infographic on the History of Email Archiving!