Google introduced “Message Log Search,” feature, which delivers the search and analysis capabilities normally available with on-premise solutions, but without associated complexity or maintenance. When messages pass through Postini service, header and transaction data about these messages is stored in a log. Previously, admins only had access to this data through customer support. With MLS feature, email administrators can now easily run searches on these logs and drill down to details about how specific messages were processed. For e.g., admins can view disposition of messages, such as whether a message or group of messages was delivered, quarantined, archived, or encrypted. Say an admin was checking the delivery status of all inbound emails from Matthew Smith. MLS returns results which include who received the message, date/time, disposition, and more.
More info: Google Postini Services