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Log in as a user with the 'Jira Administrators' global permission.
Navigate to Admin menu → Manage apps → Communities.
Go to the Product Setting page.
Enable desired functionality → press Save.
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Public Access
When Public access is enabled, external users will be able to self-register and create an account in Jira Internal Directory. Those users will not have access to your Jira instance and DO NOT count towards your license limit.
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If checked Portal Admins can allow users to access Communities without having an account. Anonymous users can view Posts created by other users, attachments, current statuses and public comments. Anonymous users cannot add new Posts, comment , and vote and search within the Portal.
Portals
List of projects for which Communities is enabled.