Forum Discussion

Mikey_O's avatar
Mikey_O
Copper Contributor
Jun 25, 2024

Email sent from Shared Mailbox gets stuck in Outbox

Hello,   I am working with a client who has a primary and shared mailbox in Outlook. They are using the newest version of classic Outlook desktop app and they have full permissions to the shared ma...
exchange
office 365
outlook for windows
Ahmed_Masoud97's avatar
Ahmed_Masoud97
Steel Contributor
Sep 10, 2026

Test classic Outlook in Safe Mode using outlook.exe /safe, then send as the shared mailbox. If it works, disable the Mail Manager COM add-in and retest, because the client-only behavior points to an add-in or local synchronization issue rather than mailbox permissions.

Keep Cached Exchange Mode enabled, but clear Download shared folders under Account Settings, Change, More Settings, Advanced, then rebuild the OST. Microsoft documents that caching secondary mailboxes can cause synchronization problems. Also check HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences for DelegateSentItemsStyle; after backing up the registry, remove it or set it to 0, and use the server-side MessageCopyForSentAsEnabled setting if copies must be stored in the shared mailbox.