A shared mailbox used for order administration is organized by region, country, customer, and year, and grew to 12,394 folders. Around September 8–9, the folder tree began stopping at roughly 976–1,000 folders in classic Outlook cached mode. Folders beyond that point are absent rather than collapsed or greyed out.
The same behavior appears in new Outlook and in the web app when the mailbox is automapped or added as a shared mailbox. The complete hierarchy is visible in classic Outlook with "Download shared folders" disabled, and through the web app's option to open another user's mailbox, so the server-side data is intact.
Permissions, automapping, hierarchy corruption, orphaned folders, cycles, excessive depth, and OST damage have been ruled out. I also deleted 9,993 verified-empty folders, reducing the total from 12,394 to 2,401, but the sync still stops at about the same point. The mailbox has Full Access assigned directly, and there are no folder-level permissions on the root or Inbox.
There is documentation about a 500 shared-folder limit and an announced increase to 5,000, but the behavior I'm seeing looks like an enforced limit near 1,000. Has anyone else noticed this after recent Outlook changes? What limit is actually active now? Also, does new Outlook have an equivalent to "Download shared folders," and what is the intended solution for large shared mailboxes once classic Outlook is retired?
3 Answers
Online archive licensing and retention policies will not solve this particular problem. They move messages, not the folders themselves, so the primary mailbox hierarchy remains just as large. To reduce the hierarchy count, folders have to be consolidated or removed. I would avoid rebuilding working OSTs or moving users to a new Outlook profile until the folder structure is reduced, because a working cached profile may only be hiding the limitation.
The web app’s “Open another user’s mailbox” view appears to be the reliable way to see the complete hierarchy, but it is not a great replacement for a team that works in the mailbox all day. New Outlook is effectively the web experience in a desktop wrapper, and it does not seem to offer a matching setting that disables shared-folder caching. For a long-term fix, this kind of filing structure should probably move to SharePoint or another document-management system rather than continuing to grow inside a mailbox.
I agree that the mailbox is being used like a file server. We found that flattening the structure to the customer level would let 47,161 messages fit into about 426 folders, while SharePoint with metadata is the better long-term design. The immediate problem is that the mailbox worked for years and then began failing on a specific date, even after removing thousands of empty folders.
The important distinction seems to be hierarchy synchronization rather than folder display. Existing classic Outlook profiles that already downloaded the complete hierarchy can continue showing it because their cached copy remains intact. New Outlook, or a rebuilt classic profile, starts a fresh synchronization and stops around the current ceiling. That would explain why some users suddenly report a problem while others insist everything still works.
That matches the behavior exactly. Moving users to new Outlook exposed the issue, and switching them back to classic did not help because it triggered a new sync. After deleting empty folders, the sync reached farther through the tree, but the ceiling remained around 1,000 items in traversal order rather than being a depth or per-branch limit.
Exactly. The archive reduced mailbox content but did nothing for folder count. The safest short-term approach is to preserve profiles that already have the full tree, while redesigning the structure and moving users toward a proper document-management system.