Reference:
https://www.cisco.com/c/en/us/td/docs/security/esa/esa12-0/user_guide/b_ESA_Admin_Guide_12_0/b_ESA_Admin_Guide_12_0_chapter_0100000.html#con_1482874 False positives are legitimate messages that are incorrectly identified as spam by the Cisco ESA. Organizations may want to implement a spam quarantine to reduce the risk of losing false positive messages and allow users or administrators to review and release them2. Reference = User Guide for AsyncOS 12.0 for Cisco Email Security Appliances - GD (General Deployment) - Spam Quarantine [Cisco Secure Email Gateway] - Cisco