In Exchange Server 5.5, Microsoft has enhanced the Internet Mail Service (IMS) with some features that tighten security for Simple Mail Transfer Protocol (SMTP) messaging. In Exchange 5.5, you can prevent SMTP clients and hosts from accessing the IMS, and you can encrypt SMTP connections.

As the Internet grows and connectivity bandwidth becomes less expensive, more companies are using the Internet as a network backbone to connect geographically dispersed networks. This configuration exposes the network to security risks that are less pervasive on a private network.

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