Summary

Portal only customer receives the mentioned notifications even he's the request participant.

Steps to Reproduce

1. Create a portal only user
2. Go to Project settings > People, add the user to Service Desk Team role
3. Create a new ticket (make sure the user created on Step 1 is not Reporter or Request Participant)
4. Attempt to mention the user in the ticket

Expected Results

Portal only customer shouldn't receive any notifications when he's not the request participant.

Actual Results

Portal only customer receives both internal and external mention notifications.

Workaround

Remove the user from Service Desk Team role