Quarantine holds a message away from normal delivery because a security or policy system wants review or delayed disposition.
Quarantine can contain spam, phishing, malware, DLP matches or administrative-policy hits.
Release is a security action
Who can release a message matters. Allowing end users to release high-confidence malware is a different risk than letting them recover bulk mail.
Keep enough metadata to understand why the message was quarantined and which policy made the decision.