If you are using Exchange or Hosted Exchange you can create a public folder that can be seen and accessed by all partys that you grant permissions to. You may also configure a rule based upon who and where the message was sent to or from to automaticly move the message to the public folder. If that is to random than you can also create a rule to filter it by subject and make sure that all of the messages has the subject of something like [project]-fill in the blank here.