Mac OS Download Page Mac Operating Systems FirstClass Client 10 10.5.2 - 10.5.8; 10.6.1 FirstClass Client 9.1 10.4.6 - 10.4.9; 10.5.2 - 10.5.8 FirstClass Client 9.0 10.3.4 - 10.3.9; 10.4.6 -10.4.9 NOTE:  If the Operating System is not explicitly mentioned, it is NOT supported To download the 10.0 Client for Mac OS X click here. To download the 9.1 Client for Mac OS X click here. To download the 8.1 Client for Mac OS 9 click here. Once the installation is complete click here. When the Login screen appears, simply enter your user ID and password and click Login.            For more information about the 10.0 Client for Mac OS X click here. For more information about the 8.1 Client for Mac OS 9 click here. Visit the FirstClass web site to download international clients.