Is Dropbox a valid means of service? It might be if it is agreed, or the documents are in fact downloaded by the recipient. But don’t count in it. In Conveyor & General Engineering Pty Ltd v Basetec Services Pty Ltd and Anor  QSC 30 an adjudicator’s determination was found to be of no effect because of the adjudicator’s error as to the validity of service led him to deny the respondent an opportunity of making a response.
The judgment of 7th March 2014 is at http://www.austlii.edu.au/cgi-bin/sinodisp/au/cases/qld/QSC/2014/30.html.