Hello, I have read various forums and websites and it seems as though many people have a problem with the mysterious envelope with the green "i"
Well, I had that issue but I found out how to fix it. I had an app called SMS Pop Up and a bunch of my messages had that stupid notification, but when I uninstalled the app it went away! Voila, problem solved this was happening to me on the Verizon Motorola Droid. Since I have uninstalled it, I have messaged various contacts and it has yet to shown itself again. I hope this helps!