Understanding that Postini uses IP based routing and not hostname is the key here, and only one instance of a unique IP or range can be used. With O365 using a shared IP class, this hinders the use of outbound and journaling services. If I recall, only E3 & E4 allow for advanced routing and most of the requests we are getting is from E1 & E2 clients. As already stated here, the work around at this time, is to set up a separate SMTP relay that has dedicated IP or range unique to the domain.