Inactive mailboxes were first introduced almost two years ago in Exchange Online. They are a free and easy way to make sure mailbox data is preserved in order to meet legal requirements. And they are directly exposed to the eDiscovery, unlike other solutions.
Now, Microsoft has made some improvements that make the feature even greater. The first set of improvements is around recovering data from Inactive mailboxes, either by converting the mailbox to regular one or by using the New-MailboxRestoreRequest cmdlet to copy its content to another mailbox (or archive). The second set of improvements is around changing the hold duration for Inactive mailboxes. As (wrongly!) advertised by the blog article above, content of Inactive mailboxes could only be preserved indefinitely and they were not being processed by the Managed Folder Assistant (which explained why time-based holds were not possible). Now, you can run the Start-ManagedFolderAssistant cmdlet against Inactive mailboxes as well (note that it will only respect retention tags with the Delete action, not Move to archive) and you will also be able to change the hold duration.
Here are the new TechNet articles:
Inactive mailboxes in Exchange Online – Overview of the inactive mailboxes functionality, the ‘landing’ page. Updated to reflect the fact that time-based holds are respected and not changed into indefinite ones.
Manage inactive mailboxes in Exchange Online – Instructions on how to make a mailbox Inactive.
Recover an inactive mailbox in Exchange Online – Steps to use New-Mailbox –InactiveMailbox to “convert” an inactive mailbox to an active mailbox. This will remove any holds placed on the mailbox and put it on a 30 days retention hold, to make sure the user will have time to review the content before it’s deleted or moved to the archive. The contents and folder structure of the inactive mailbox are retained, and the mailbox is linked to a new user account. In addition, the single item recovery period is set to the maximum value of 30 days, again to minimize the chance of data loss. It’s important to place the newly recovered mailbox under hold if it’s necessary to meet legal requirements.
Restore an inactive mailbox in Exchange Online – Steps to use New-MailboxRestoreRequest cmdlet to copy/merge the contents of an inactive mailbox to an active, target mailbox. Inactive primary and archive can be restored to either the primary or archive in the target mailbox. The inactive mailbox is still available/accessible after it’s restored, and you can repeat the restore process to another mailbox if necessary. No automatic litigation/in-place/retention hold is placed on the target mailbox.
Remove a hold from an inactive mailbox in Exchange Online – Instructions on how to remove all holds from an Inactive mailbox.