Update submissions-outlook-report-messages.md

Added a missing information. 
Reason : When users report an email as Junk using the built-in Report button, the sender of that email is automatically added to the user's Blocked Senders List. This behavior occurs consistently across different clients and tenant configurations but has not been documented in any public-facing materials.

Author: MithunRathinam

defender-office-365/submissions-outlook-report-messages.md

@@ -74,7 +74,7 @@ In a supported version of Outlook, select one or more messages, select **Report*
 
 Based on the [User reported settings](submissions-user-reported-messages-custom-mailbox.md) in your organization, the messages are sent to the reporting mailbox, to Microsoft, or both. The following actions are also taken on the reported messages in the mailbox:
 
-- **Reported as junk**: The messages are moved to the Junk Email folder.
+- **Reported as junk**: The messages are moved to the Junk Email folder, and the sender is automatically added to the user's Blocked Senders list. 
 - **Reported as phishing**: The messages are deleted.
 
 ### Use the built-in Report button in Outlook to report messages that aren't junk