Although service has improved dramatically in recent years, warnings about delays and disappearances of incoming and outgoing mail apply to St Petersburg. Airmail letters and postcards take up to two or three weeks to Europe, and up to three or four weeks to the USA or Australasia.
To send parcels home, head to the elegant main post office. Smaller post offices may refuse to send parcels internationally; most importantly, your package is more likely to reach its destination if you send it from the main post office. You will need to provide a return address in St Petersburg – your hotel name will be fine.