I have been using Earth Class Mail for years and I love it. Using the web interface I can look at envelope scans of my mail. I can then press a button to have them open an envelope and scan the contents for me to read online, saving the need to forward it physically. If I want it forwarded physically, they'll also do that too.
I have not used it to forward mail to Argentina (I'm new here), but I have forwarded several small packages to Uruguay without problem.