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From Jira 8.19 onwards, users must have proper licenses and application access to receive email notifications. If users are removed from the access group, they won’t get notifications, even if they're involved in an issue (e.g., assignee or reporter), regardless of the notification scheme.
In Jira 8.20.6 and higher, a dark feature flag allows reverting this behavior: com.atlassian.jira.send.email.notifications.to.user.without.application.access.enabled
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