Users are intermittently receiving a "no permission" error when trying to send new messages as at least two shared mailboxes. Full Access and Send As permissions appear correct, and the issue only started recently. Sending from Outlook on the web works normally, while desktop Outlook sometimes sends successfully and sometimes changes the message to "sent by [user] on behalf of [shared mailbox]." Replies to existing messages do not seem to be affected. The environment is hybrid, and rebuilding OST files and running an Office repair did not help. Has anyone found a reliable fix?
4 Answers
Because this is a hybrid environment, verify that the Send As and Full Access permissions are present and synchronized on both the on-premises and cloud sides. A permission can look correct in one place while the other side still has stale or missing data.
Check whether anyone is using the new Outlook desktop client. It has had several issues with shared mailbox permissions, so switching back to classic Outlook is worth testing even if only one affected user is on the newer version.
The affected users are on classic Outlook, although I’m using the new client myself and haven’t seen the same Send As problem.
Since it works in Outlook on the web, the mailbox permissions are probably valid and the problem is isolated to the desktop Outlook client or its cached recipient data. In a new message, remove the automatically completed address from the From field and type the shared mailbox address manually before sending.
Remove the user’s Send As and delegate permissions completely, wait about 15 minutes for the change to propagate, then add the permissions back. After another short wait, restart Outlook and test again. This can clear stale permission data.
Someone may already have tried that, but we’ll confirm whether the permissions were removed long enough for replication to complete.
That’s possible, although the main affected user has owned the shared mailbox and had access for years. The web client still works, so we’ll check synchronization and replication anyway.