Outbreak Filters provide zero-hour protection by leveraging Cisco Talos intelligence, reputation data, and behavioral analysis. They can detect and quarantine suspicious messages during emerging malware campaigns before traditional anti-virus vendors release updated signatures.

Bounce Verification is a feature that mitigates denial of service attacks on Cisco ESA. A denial of service attack is an attempt to overwhelm a system or network with excessive traffic or requests, rendering it unavailable or slow for legitimate users. Bounce Verification prevents Cisco ESA from accepting bounce messages that are not generated by itself or by trusted hosts, reducing the load on the system and preventing backscatter spam.
https://www.networkworld.com/article/2305394/ironport-adds-bounce-back-verification-for-e-mail.html

https://www.cisco.com/c/en/us/td/docs/security/esa/esa13-0/user_guide/b_ESA_Admin_Guide_13-0.pdf p.675

When a message is identified as spam positive, the anti-spam action takes precedence and the message is placed only in the spam quarantine, even if outbreak filters also detect it as outbreak positive.