Last September, we officially announced the increase of the supported limit of Public Folders in Exchange Online from 100,000 to 250,000. In line with our efforts to scale Public Folders even further, we are glad to announce that Exchange Online now officially supports public folder hierarchies of up to 500K public folders in the cloud – double the previously supported limit of 250K public folders!
What does this mean?
All existing customers using Exchange Online who are currently constrained by the limit of 250K public folders, can now expand their Exchange Online public folder hierarchy up to 500K folders. The current Exchange Online limits can be viewed here.
Note about migrations: Exchange 2013/2016 customers can still only migrate up to 100K public folders to Exchange Online, and Exchange 2010 customers can only migrate up to 250K public folders to Exchange Online. However, once folders are migrated to Exchange Online, you can expand the hierarchy up to 500K public folders. We are working to resolve these limitations in the future. Edit 10/30/2018: Exchange 2013/2016 customers can now migrate up to 250K public folders to Exchange Online, please see this post.
Keep checking this blog for further updates on the subject. In case of any questions, please ask via the comments section below. Public folder team