You have a mixed Microsoft Exchange Server 2003 and Microsoft Exchange Server 2007 environment.
The journaling feature is enabled for Exchange Server 2003 recipients and for Exchange Server 2007 recipients.
The journal mailbox is located on an Exchange Server 2003 server.
Messages must traverse multiple Exchange Server 2007 Hub servers to reach any Exchange Server 2003 recipients.
In this scenario, Exchange Server 2003 journals the messages. Therefore, Exchange Server 2003 duplicates the journal reports.
This issue occurs because Exchange Server 2007 removes the EXCH50 binary large object (BLOB) from a message when the message passes through more than one Exchange 2007 Hub server. The EXCH50 BLOB lists the journal recipient GUIDs for which an Exchange Server 2003 server has already generated a journal report. Because Exchange Server 2007 removes the BLOB objects, Exchange Server 2003 does not receive this list. Therefore, Exchange Server 2003 determines that the message has not been journaled and then creates new journal reports.
To resolve this problem, install the following update rollup:
972076 Description of Update Rollup 2 for Exchange Server 2007 Service Pack 2
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.