Message splintering is a process that occurs when configuring separate incoming mail policies on Cisco ESA. Message splintering means that Cisco ESA will split a single incoming message into multiple copies, each with a different recipient and policy, and apply different security services and actions to each copy.

Reference:
https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/117972-technote- esa-00.html

To enable LDAP recipient verification on a Cisco Secure Email Gateway appliance, you need to configure the LDAP query on a listener and configure LDAP server profiles. The LDAP query specifies the criteria for matching recipient addresses against an LDAP directory. The LDAP server profile defines the connection settings and authentication credentials for accessing an LDAP server2. Reference = User Guide for AsyncOS 12.0 for Cisco Email Security Appliances - GD (General Deployment) - Configuring LDAP Queries [Cisco Secure Email Gateway] - Cisco

Spam Quarantine End-User Authentication Query is a query that Cisco ESA performs against an LDAP server to validate the end-user credentials during login to the End-User Quarantine.