If your Customer Permission allows anyone - "Who can access the portal and send requests", everyone who has an account on your site would have access to the portal so they will be added into the customer list.
If those users are no longer needed, you would need to remove them from the user management - https://YOURSITE.atlassian.net/admin/jira-service-desk/portal-only-customers
Alternatively, you could also change the permission to Customers my team adds to the project.
Hope this helps.
Hello Community 👋, I'm a product manager at Atlassian, looking at improving change management capabilities across our products. In particular, we're looking at bridging the gap between Dev & ...
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