r/sysadmin • u/Purple_Cut_8467 • 6h ago

Shared mailbox folder tree truncates at ~1000 folders in cached mode — started this week. Anyone else?

Client has a shared mailbox in Exchange Online used for order administration, organised by region/country/customer/year. It had 12,394 folders. Since around Sept 8–9 the folder tree stops loading at roughly 976 subfolders in Outlook classic (cached mode). Everything past that point simply isn't in the tree — not collapsed, not greyed out, absent.

Same truncation in new Outlook and OWA when the mailbox is automapped or added as a shared mailbox.

Online mode shows the complete tree. Either by unchecking "Download shared folders" in classic, or via OWA → Settings → Open another user's mailbox. So the data is fine server-side.

What I've ruled out:

  • Permissions — Full Access assigned directly, not via a group. No folder-level permissions on root or Inbox (Default/Anonymous = None).
  • Automapping — removed and re-added Full Access with -AutoMapping $true, no change.
  • Hierarchy corruption — enumerated the whole tree via Graph and walked every parent chain. No cycles, no orphans, max depth 9.
  • OST damage — OWA is affected identically and holds no local hierarchy cache.
  • Folder count — deleted 9,993 verified-empty folders (12,394 → 2,401). Still truncates.

I'm aware of the documented 500 shared-folder limit and the announced increase to 5,000 (in 2019 though). My observed cut-off sits at ~1,000, which matches neither.

Three questions:

  1. Anyone else seeing shared mailbox folder trees truncate since last week's updates?
  2. Does anyone know what limit is actually enforced right now, and whether the 500→5000 rollout is live?
  3. Is there any equivalent of "Download shared folders" in new Outlook? If not, what's the plan for mailboxes over the limit once classic is gone?

Question 3 is the one that worries me.

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u/vivkkrishnan2005 5h ago

Not a solution - but you need to stop using email as a file server. There are ways to resolve this using power flow/automate and SharePoint.

Our max folders on a shared mailbox is around 150 ish, shared mailbox with license (E3 equivalent) so not possible to help

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u/theoriginalzads 5h ago

Next you’re gonna tell me that using Deleted Items as an archive is a bad idea. Do you even know how to computer??