Customers can reply to any of their tickets from the customer portal, including closed tickets. A customer replies like this:
Open the ticket.
Type the reply in the reply box.
To attach a file or image, click the T icon to show the formatting toolbar, and use its attachment or image button.
To add someone in CC, click Cc and enter their email address.
Click Send reply.
To reply and close the ticket at the same time, open the menu on the Send reply button and choose "Send and close". This option isn't there when the ticket is already closed.
The reply appears on the ticket in NeetoDesk under the name of the person who sent it. Your team gets the same notifications, and the same automation rules run, as when a customer replies by email. For example, if your workspace has the default automation rule "[Status Update] - Mark as Open when original requester replies", a reply from the customer who raised a closed ticket reopens it.