The system was designed in an era when there were many email formats and services, including online services such as CompuServe and AppleLink, networking standards like X.400 and SMTP (Internet mail), and LAN-based servers such as Microsoft Mail and QuickMail. In order to support this diverse environment, AOCE includes a robust layered protocol stack that, in theory, can be used with practically any store-and-forward type of environment. This is used within AOCE not only to service mail, but faxes, printing and even directly sending files from one machine to another without enclosing them in a mail message or needing a file server.