Load balancing and failover are two configurations that can be used on multiple LDAP servers to connect with Cisco ESA. Load balancing means that Cisco ESA will distribute the LDAP queries among the available LDAP servers in a round-robin fashion, improving the performance and efficiency of the LDAP queries. Failover means that Cisco ESA will switch to another LDAP server if the current one is unavailable or unresponsive, ensuring the continuity and reliability of the LDAP queries.
Reference:
You can enter multiple host names to configure the LDAP servers for failover or load-balancing. Separate multiple entries with commas.

The type of attack that is prevented by configuring file reputation filtering and file analysis features is zero-day. Zero-day attacks are those that exploit unknown vulnerabilities in software or systems before they are patched or fixed. File reputation filtering and file analysis features help to protect against zero-day attacks by checking the reputation of files attached to email messages and sending them to a cloud-based service for dynamic analysis.

https://www.cisco.com/c/en/us/td/docs/security/esa/esa13-
0/user_guide/b_ESA_Admin_Guide_13-0.pdf P.129

You can enter multiple host names to configure the LDAP servers for failover or load-balancing. Separate multiple entries with commas.
Reference:
https://www.cisco.com/c/en/us/td/docs/security/ces/user_guide/sma_user_guide/ b_SMA_Admin_Guide_ces_11/b_SMA_Admin_Guide_chapter_01010.html

Explanation/Reference: https://www.networkworld.com/article/2305394/ironport-adds-bounce-back-verification-for-e- mail.html