Dated Ticket Emails / New Ticketing Application

We are in the process of migrating to a new ticketing application over the next 6 weeks.

For existing open tickets, we plan to move them to the new application.

We are particularly interested in guidance on how to best redirect a customer to the new instance if they are responding to a ticket email generated in the previous system.  To achive this we are planning on leveraging

• Reports to look for anything generated post launch.
• Updating email notifications to redirect the customer to the new client portal and resubmit.

Do you have any other recommendations to guide users toward the new system if they are responding to a ticket from the previous ticketing application (whether it is a migrated ticket or a dated closed ticket).  We want to make sure that any responses to the original system are not lost. 

Thank you for your time.