Users are intermittently receiving a "no permission" error when trying to send new messages as shared mailboxes. The issue affects at least two shared mailboxes and started recently, even though Full Access and Send As permissions appear correct. Sending from the web client works, while Outlook desktop sometimes sends successfully and sometimes changes the message to "sent by [user] on behalf of [shared mailbox]." Replies to existing messages seem unaffected. The environment uses hybrid Exchange, and rebuilding OST files and running an Office repair did not help. Has anyone found a reliable fix?
4 Answers
In a hybrid Exchange setup, verify that the Send As permission is present and synchronized on the correct side. The permissions can look correct in one management interface while the corresponding object or ACL has not fully synchronized. Also make sure users are using the classic Outlook client if the newer desktop interface is enabled, since it has had issues with shared mailboxes.
When creating a new message, remove the automatically populated address from the From field and type the shared mailbox address again, then select the correct directory entry. Outlook may be using a stale cached address or resolving the mailbox incorrectly.
I’ll have the affected users try reselecting the From address instead of using the cached entry.
Remove the user’s Send As and delegate permissions completely, wait around 15 minutes for the change to propagate, then add the permissions back. Wait again, restart Outlook, and test with a new message. This can clear stale permission data.
Someone may already have tried that, but I’ll confirm whether they followed the waiting period between removing and restoring the permissions.
Since sending works in the web client, compare that with Outlook desktop first. That points more toward Outlook’s cached permissions, profile state, or address resolution than the mailbox permissions themselves. Rebuilding the OST alone may not clear every cached identity or recipient entry.
The web version works correctly. The failures appear to be limited to new messages in the desktop client; replies are not affected.
The environment is hybrid, although one affected user has owned the shared mailbox and had access for years. The newer Outlook interface is not enabled for those users.