Post offices are scattered throughout every district in Vienna and are recognizable by a square yellow sign reading "Post." They are usually open weekdays 9-noon and 2-6, Saturday 8-10 AM. The main post office, near Schwedenplatz, is open 6 AM-10 PM daily, and the offices at the South and West railway stations are open until 10 PM weekdays, 8 PM weekends.
You can have mail held at any Austrian post office; letters should be marked Poste Restante or Postlagernd. You will be asked for identification when you collect mail. In Vienna, if not addressed to a specific district post office, this service is handled through the main post office.
Main Post Office (Fleischmarkt 19, A-1010, Vienna).