Google Message Security for Google Apps Administration Guide - Manual (Page 159)

Quarantine Summary & Notifications 159
The Quarantine Summary is sent to the user’s primary email address, or notice
address. If there are no spam or virus messages quarantined, no Quarantine
Summary is sent. The default message looks something like this:
Accessing Messages from the Quarantine Summary
The Quarantine Summary links to the Message Center and each individual
message.
Users can access the Message Center by clicking the Message Center link in
their Quarantine Summary messages. Or, they can go to the following URL:
login.postini.com/a/your_domain
Note: Users should replace your_domain with the domain you use for Google
Apps, such as jumboinc.com.
Users must be logged in to their Google Apps accounts to access the Message
Center.