Enable/Disable Messages Features
The Messages module must be enabled for it to appear for a given workspace. Click on a workspace name from the drop-down list at the top left of the screen. Click the Settings link at the top of the screen. On the left menu, click on Features to Display under Settings – This Workspace. Under the Messages row, in the ENABLED FEATURES column, you can click the checkbox for either row to enable/disable the Posts or Channels & Direct Messages features of Messages. If you would like Reviewer or Partner users to also see the features, check the boxes for those columns.
The Messages module will appear at the top of Workzone.