Jsezze
osTicket is an email based system. With that being said, you can disable the email activation by setting the User Registration Method setting to "Disabled - all users are guests". 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. There are some emails you simply cannot disable unless you modify the code such as the System Errors sent to the Admin, password reset emails, etc.
Cheers.
