There is a system for new portal messages to be sent for review. As far as I can see there is, however, no way to mandate a review. The only task permission I can see is to allow a user to send a portal message or not.

There should be a task permission to 'Draft a message' seperate to 'Sending a Message' or perhaps one which says that the message must be reviewed. Perhaps this could be linked to a responsibility type such as partner and manager of that client, or maybe using the reports to... . Ideally there needs to be something in place to ensure messages are reviewed by somebody appropriate and not just another colleague in the same room. There ought to be more than one person available on the list of reviewers in case one is away. Perhaps it could be someone who appears on the list of partners under Maintenance > Internal > Partners