"They dont have any agent account , they are just replying to the email from their email account not in OSticket."If they are not an agent, and not a collaborator then it is working like it should be. They are not associated with the ticket, and not an agent."As you are saying to change the subject line with tickets numbers , this can be done in OSticket or my email account. if its in OSticket please let me know where can i make the changes."Admin panel -> Emails -> Templates.