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