You are attempting to release a quarantined email by Scan-time Protection Policy, but the email keeps getting quarantined again after the release.
Email Security.cloud
This behaviour is intentional and designed this way. For example, if an email was quarantined because it contained a URL categorized as malicious, it's considered a legitimate detection rather than a false positive. Therefore, allowing users to release emails with such URLs could potentially expose them to malicious or phishing content.
If you want to prevent specific URLs from being quarantined, adjust the scan-time protection policy. You can do this by changing the policy's action or excluding the specific category from its scope.
The customer can review the URL category and submit the URL to re-categorize it or submit the email sample as False Positive for further investigation: