The Chilean postal service is called CorreosChile. While it is basically comprehensive and sufficient, it does leave a little to be desired.
Postage times can be slow at times and are often inconsistent. A parcel from the U.S.A. arrived in less than two weeks; a friend of mine sent two postcards internationally (at the same time, to the same place) that arrived two weeks apart. If you are sending non-important items, like postcards, this service is cheap and easy. Prices are fair – to send a postcard internationally costs $430 (around $0.90 USD). There are locations all over the place – just look out for the red and white logos and you’ll never be far away.
However, if you need to make sure that your important documents arrive at the destination in a safe and timely fashion, you might want to invest in courier postage. There are a few choices – DHL, Chilexpress and FedEx. Check out the websites to find your nearest office. It’s very expensive (I wanted to send a two-page form back to Australia and was quoted $45 USD – no thank you!) so decide carefully.