I am running Mac OS X Mountain Lion (10.8.4) and the application doesnt even open. It just crashes and asks me to send the information to Apple. I discovered you have to disallow contacts from being accessed. When you get the app to open the envelope doesnt even print the correct direction. It doesnt print sideways either so unless if you have a fancy printer that can print Enevelope #10 the long ways. This is nothing more than the pointless letter feature in Microsoft Word but as a seperate over priced application. If I could just be able to rotate the envelope so I can print it out then I can probably rate this app as a 4/5 stars easily. But since it cant even do that I have absolutely no use in this application. This application is worthless. -Mike