My former employer was set up to all support customers to only send emails to the support inbox, and then have that inbox redirect to NS. The customers never saw the NS email addresses and most of them did not even know we used NS. I am trying to replicate that setup.

The current situation: We are currently creating cases by redirecting emails from our support email address to the Netstuite support address, and that works correctly.

NS sends back a case notification with an email address unique to the case. However, our users are uncomfortable with that long and unfamiliar address and email back to our support email address. We tried to redirect those emails back to NS, and have them be attached to the correct case in the system. Unfortunately, each of these redirected emails creates a new case.