LDAP Authentication and Synchronization
In Spam Experts both LDAP Authentication and LDAP Mailbox Sync use LDAP to query your company user directory.
LDAP Authentication allows users to access their personal Spam Experts control panel using their company credentials. This is useful so that your users can access their mail in a business continuity scenario (if your directory is maintained on a separate server to your mailboxes). See Set up LDAP Authentication.
LDAP Mailbox Sync
LDAP Mailbox Sync keeps the Local Recipients list in sync with the users listed in the company directory. This allows you to enable local recipient only delivery without having to maintain the list manually. See Configuring LDAP Mailbox Sync.