Once an incident is set to Resolved state, the customer will receive a notification like this:

If the customer replies to this message within 5 days, the Assignee receives an email notification that the customer responded, but the ticket state is not changed.

To trigger a change on the incident state and stop the 5 day countdown to closure, the customer needs to click the "Not Resolved" link as instructed in the notification. This will open a new email with a reference to the incident. When the customer sends the email with their update on why they need additional help, this update will be added to the incident, and the incident will be moved to Assigned state.

If the customer does not respond, the ticket will automatically be placed in Closed state, at which point it cannot be reopened. If the customer needs additional assistance, a new ticket will need to be created. 

If a customer responds to a ticket that is Closed, they will receive the following notification with instructions to submit a new ticket and reference their closed ticket number: