Google Apps Directory Sync for Postini Services Administration Guide - Manual (Page 26)

Configuration 29
Message Security Service Settings
The Message Security Settings section governs how the directory sync utility
connects to the message security service, and how the directory sync utility
generates your message security service user list for comparison.
Before you enter information in the Message Security Service Settings pages,
collect the information from the message security service. You may need to create
new organizations or administrators in the message security service.