Step 3: Activate Unread Ticket Tagging

After you place your image tag, please go to Admin->Workflows->Automations->Ticket Updates :

1. Click on New Rule and name the rule: Unread Ticket Tag.
2. Under When an action performed by select Agent & Any.
3. Under Involves any of these events add "Reply is sent" from dropdown.
4. Under on tickets with these properties: Leave it as-is, no updates needed
5. Under perform these actions: Add tag and name it unread.
6. Click the Save button.

Here is an image of how your Observer Rule should look: