Post (letters and cards) are sent by the Colombian Servicios Postales Nacionales. Keep in mind, that it usually takes 1 to 2 months to reach Europe.
Internet in Colombia
Internet cafés can be found everywhere in Colombia, where you can also send mail and make inexpensive international phone calls. You can often Skype here as well. In more and more hotels free Wi-Fi is available. The same applies to a large number of bars and restaurants. See: www.wificafespots.com