The Message Queuing Service is only required on an OCS Front-End Server if you plan to use the Monitoring/Archiving Server roles in OCS (alternatively the Archiving/CDR or Monitoring roles in 2007/2007 R2). For example, the MMQS is how IMs are gathered from FE serves for archiving.Jeff Schertz, PointBridge | MVP | MCITP: Enterprise Messaging | MCTS: OCS