These steps will help you exclude a folder from syncing:

  1. Lets say you have a folder that you want to exclude called NON_CLOUD.
  2. We first create an empty folder that is renamed to NON_CLOUD and place it into Dropbox.
  3. Then, we use selective sync to unsync that folder: https://www.dropbox.com/help/175
  4. Next, move your actual NON_CLOUD folder into the previous location of the empty NON_CLOUD folder.
  5. That folder will have a grey circle with a “minus” sign and will not be synced to Dropbox.