As of the option is also available from shared mailbox where you have the right to send from it ( send as or send on behalf), not where you only have read access
In Outlook
Open the mail in outlook (at least in the read panel)
A button is available in your toolbar: "the report message". Click on it
Based on the content of the message, select of it's pure spam (junk) a phishing attempt or "not junk" if you estimate is was incorrectly flagged as spam.
In Outlook on the web
Open the mail in outlook in the read panel
Click on the 3 dots icon and select the appropriate option
If you have opened the mail in full screen, the option "junk" is also available in the toolbar.
What we do with what you flag?
If you report it, we will review it and confirm the junk/phishing attempt.
If it’s a phishing attempt, we can then directly block similar email, attachment, or URL to avoid any issue for other user.
You will receive later on a message from “Submissions@messaging.microsoft.com” with the title of the mail you have submitted and the result.
As there is a rule on server side that move everything into the Spam folder when it contain “[SPAM]” in the subject, the message of confirmation will be moved to the junk folder if it was already flagged as spam before.
Example below:
Thank to your action we can make our environment more secure.