When Ticket closed by sending an e-mail to the customer results in bounce e-mail or if customer replies, the Ticket gets re-opened.
SAP Cloud for Customer
Reproducing the Issue
You have closed Ticket ABC (ABC represents Ticket ID) by sending an e-mail to customer. Notice the Ticket was re-opened if the e-mail resulted in bounced e-mail notification or when customer replied.
If customer has some question/concern about the closed Ticket, they should be able to respond and keep the Ticket open. The same applies for bounced e-mail scenario where the customer did not receive the final answer.
This is the system standard behavior.
E-mail, Bounce, Customer, Ticket , KBA , LOD-CRM-EMP , Employee , How To