All mail goes by air, so there's no supplement on letters or postcards. Within Europe a letter or postcard of up to 20 grams (about ¾ ounce) costs €0.65; to the United States or Canada, it’s €1.40. Up to 50 grams costs €1.30 for Europe and €2.05 for the United States or Canada. If in doubt, mail your letters from a post office and have the weight checked. The Austrian post office also adheres strictly to a size standard; if your letter or card is outside the norm, you'll have to pay a surcharge. Always place an airmail sticker on your letters or cards. Shipping packages from Austria to destinations outside the country can be expensive.
You can also 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.
For overnight services, Federal Express, DHL, and UPS service Austria; check with your hotel concierge for the nearest address and telephone number.