Yes, for created ticket, it's allowed customer to reply via your email system, and add member in mail COPY loop whoever OWN or NOT OWN ticket account.

And after ticket replied, he/she could see the ticket thread in his/her email system.

In case same company staffs own ticket accounts, then everyone in same company could see created ticket on ticket system via log in.

If any new comer cannot see created ticket by other staff, please feel free to inform us to group the new comer in your company group.