As far as I know, osTicket is an email-based system. For security reasons, when a user opens a ticket for the first time, he must obtain the ticket number through a valid email address. The user can use the email address as the username and the ticket number as the Password login query.
If your server does not support email service, you can disable the email activation by setting the User Registration Method setting to "Disabled - all users are guests".https://prnt.sc/_kE8UxxPMb9D And you can disable user alerts as well. However when you add a Reply to Tickets you must always select Do Not Email Reply manually. https://prnt.sc/vO_p239r6zzx