How Exchange Server 2003 Envelope Journaling Works
As mentioned earlier, message-only journaling sends a copy of a message to the journaling mailbox every time a user in a journal-enabled mailbox database sends or receives a message. This is not suitable for most regulations that require journaling because of compliance.
Envelope journaling provides a much more useful service because it records data about all recipients that a message is delivered to. One way to understand how envelope journaling works is in the context of distribution groups. Most distribution lists change, and query-based distribution lists are specifically created based on the fact that lists change. Therefore, just knowing that a message was sent to a specific distribution list is not sufficient to comply with most of the regulations mentioned earlier in this guide. To comply, you must show who actually received a particular message, regardless of whether they were on the Bcc line, or were a member of a distribution group that has since changed.
To provide this level of data, Exchange provides the "envelope" or P1 headers for a particular message. The envelope data is the actual recipient list that Exchange generates as a message is in transit that enables a message to reach all recipients. Unlike the P2 headers (the recipients as declared by the sender in a particular piece of received mail), the envelope data changes as it travels to the many destinations; these changes occur because of distribution list expansion and hidden distribution list behavior.
To enable envelope journaling, you must enable message-only journaling and configure a setting in Active Directory® directory service. Message-only journaling is enabled by selecting a check box on the property page for the mailbox store that you want to journal and specifying a journal recipient mailbox for all journalized data. The setting in Active Directory is a global setting that turns on envelope journaling for the Exchange organization. After you configure the setting in Active Directory, whenever journaling is enabled on a mailbox database, it will be envelope journaling.