O365 Shared Mailbox Permissions Reset for Outlook
The issue was resolved (with Microsoft support help) by re-applying Full Access permissions and removing shared mailbox Outlook auto-mapping for the affected users and then adding the shared mailbox manually in Outlook. Re-applying permission via Office 365 admin center didn’t have any effect.
- Run: Remove-MailboxPermission -Identity shared_mailbox@domain.com -User user@domain.com -AccessRights FullAccess
- Run: Add-MailboxPermission -Identity shared_mailbox@domain.com -User user@domain.com -AccessRights FullAccess -AutoMapping:$false
- -AutoMapping:$false disables shared mailbox auto-mapping to users’ Outlook profiles.
- Wait 30-60 minutes for changes to propagate until shared mailbox disappear from users’ Outlook.
- Manually add shared mailbox to users’ Outlook: File > Account Settings > Change > More Settings > Advanced > Open these additional mailboxes.
- Try sending email as the shared mailbox by selecting From: address from Online Global Address List (to prevent caching issues).