Exchange Server 2007 allows customers to flexibly configure and control inbound and outbound Internet mail flow in a way that meets the requirements of their environments. The three typical mail flow scenarios are:

  • You send and receive Internet e-mail by relaying through a subscribed Edge Transport server. A subscribed Edge Transport server has been subscribed to the Exchange organization. The Microsoft Exchange EdgeSync service that is running on the Hub Transport servers periodically synchronizes recipient and configuration data to the ADAM instance on the Edge Transport server.
  • You send and receive Internet e-mail by relaying through Microsoft Exchange Hosted Services or other third-party Simple Mail Transfer Protocol (SMTP) gateway servers.
  • You send and receive Internet e-mail directly by the Hub Transport server. This usually applies to small organizations with only one Exchange 2007 server having all the Hub Transport, CAS and Mailbox roles.

Each scenario requires specific configurations to allow proper Internet mail flow. Please view the Microsoft TechNet at http://technet.microsoft.com/en-us/library/aa998212.aspx and pick up the scenario for which your organization meets prerequisites.