Update quarantine-faq.yml

@chrisda

Author: faoquong

defender-office-365/quarantine-faq.yml

@@ -275,6 +275,12 @@ sections:
 
           **Approve release** has been retired and is now included in :::image type="icon" source="media/m365-cc-sc-check-mark-icon.png" border="false"::: **Release**.
 
+      - question: |
+          **Block sender** button in quarantine notifications or on the **Quarantine page** does not seem to be working. What's going on?
+        answer: |
+          **Block sender** action is not possible for Public folders. 
+           Public folders in Exchange do not have junk email configuration settings like individual mailboxes do. The cmdlet Set-MailboxJunkEmailConfiguration is used to configure junk email settings for mailboxes, not public folders.
+          
       - question: |
           **Filter** and **Search** aren't working. What's going on?
         answer: |