Replies from a Service Desk Customer participants are always created as internal comments when the reply made via email. Raising this as a bug because it doesn't make sense to have customer adding internal comments to the request they've raised.
- Add a customer into a ticket as a participant.
- Disable Service Desk email channel for the project you are working on.
- Ensure that the participant has permission from JIRA Permission to add comments to the ticket. If you don't do this; SD Customer can't add comments on the ticket.
- Comment on the ticket so that a notification is sent to the participant.
- Reply to the notification as the participant.
Comment will be added as a public comment.
Comment will be added as an internal comment.