If a customer sends an email to the default email address associated with my Service Desk, they get an email failure with the message in the logs of
"You don't have permission to access this service project."
If i then add the customer email first to the Customers list then the customer is able to send an email and a support ticket is created.
My settings look correct: I had thought with these settings, anyone can send an email and get a ticket filed, not just assigned customers. I believe JSM should be auto-creating the user.
On the Jira Service Management side i have

and

and on the Project settings side i have

Any ideas if there is anotehr setting somewhere i've missed?