Hi,
You can achieve this with transport rules. You will need a mail enabled security Group that the Year 1 and 2 students are member of, or you can use properties (Attributes like Title, Department etc that define the users)
1. Log in to admin portal
2. Navigate to Exchange Control Panel (Admin\Exchange)
3. Click Mail Flow in the left pane
4. Click + (add new Transport Rule), Sekect Restrict messages by sender or recipient
5. In the dialoge that appears, first click More options at the bottom
6. Now, fill in the following criterias:
- Name: As you like
- Apply this rule if: The sender is\Part of this Group or you can use The senders specific properties include any of these Words (if you want to use AD attributes instead - your choise)
- Select the Group or Properties accordingly in the dialoge that appears
- Click Add condition
- For the second condition (and), select:The recipient\is external/internal
- Select Outside the organization
- Do the following: Block the message (and select the action that best suits your intention)
- Click Save
- Test to verify
Done!
Hope this helps.