Follow these instructions when Dropbox folders you have permissions to are not showing in your Dropbox:
1. Click on the Dropbox folder link from the chat or email.
2. Once in Dropbox, click “Save to Dropbox” on the top right of the window.

3. Click "Save" in the pop up window. Now this new folder is in your list of Dropbox folders.

4. After clicking "Save," that folder is visible in your list of Dropbox folders.
It takes longer to be visible in Finder (takes longer to synch).
