Microsoft already offers unlimited archive storage in Office 365 Enterprise E3 and E4 plans. Recently, Microsoft announced Import Service to import terabytes of data from on-premises systems to Office 365, or to manage high volume mailboxes. In some cases, a customer reaches a threshold that required them to contact Microsoft support and perform manual steps to provision additional space. To fix this issue, Microsoft is now announcing new auto-expanding, highly scalable archiving.
This update retains the best-of-breed archiving experience that end users, IT pros and compliance officers love so much. End users continue to access their email data in the same way; IT pros continue to enable archiving for their users with the same user interface and PowerShell commands, and our comprehensive compliance stack—Auditing, Retention, Hold and eDiscovery—works seamlessly with the updated archiving architecture.
Read more about it here.