Google is transitioning Postini services to the Google Apps platform beginning in 2013.
Over the past year, Google have built similar Postini email security and archiving features into these Google Apps services:
Google Apps for Business : A professional suite of hosted email, calendar, and collaboration services
Google Apps Vault : Archiving and discovery services for email
With this transition, you will receive comparable email security, protection, and archiving, but through the more robust Google Apps platform.