In Exchange Server 5.5, all public folders were mail-enabled and hidden by default. In Exchange 2000 Server and Exchange Server 2003, folders can be mail-enabled or mail-disabled, depending on whether the Exchange Server organization is in mixed mode or in native mode.
Mail-enabling allows authorized users to post items to public folders by using standard e-mail. After you understand how public folder e-mail messages are routed, you can configure Exchange Server to optimize message delivery for public folders.
For detailed information about how e-mail is delivered to public folders and how you can configure Exchange Server to optimize e-mail delivery to public folders, see Exchange Public Folder Best Practices: Mail-Enabling Public Folders.