Office 365 (Outlook on the web | Outlook for Windows) - Unable to use report spam or report phish buttons on behalf of another account
In certain scenarios and depending on the Outlook client you are using, you may either not have the option to report a message as spam/phish or receive an error when you do so.
Workflow
You are attempting to submit a message as spam/phish when interacting on behalf of another account/mailbox you have access to.
Outlook on the web
The "Report Spam" or "Report Phish" buttons will not appear when viewing a message.
Outlook 2016 for Windows
When you attempt to use the "Report Spam" or "Report Phish" buttons, you receive the following error - "You cannot perform this action. Add-ins are not supported in this folder."
Reason for this error/issue
Microsoft has confirmed that add-ins only work on the default account you are logged in with (authenticated). If you would like to have this feature enabled for shared accounts/mailboxes, please review the following user voice thread.
Workaround
If you want to submit a message as spam or phish, please follow the instructions in the Office 365 - Submit a message as spam/phishing document within the "Outlook on the web (do not use Outlook desktop client)" section.