10.1 Introduction

The new routing architecture in Exchange 2000 is based on SMTP and makes use of a proven routing algorithm. In this chapter, we will discuss how all of this magic works. For starters, let's look at a simplified view of the architecture (see Figure 10.1).

Figure 10.1: Exchange 2000 messaging architecture

10.2 SMTP Core Transport

Simple Mail Transfer Protocol (SMTP) is the default protocol used for the transmission of messages between Exchange 2000 servers. The protocol is well established and was first defined in RFC 821 in 1982. (One of the better sources for messaging related RFCs is the Internet Message Consortium at http://www.imc.org/.) The Exchange 2000 and Windows 2000 SMTP service were also developed using the Internet draft that eventually became RFC 2821, which was actually released after the Windows 2000 SMTP shipped.

As mentioned previously, until Exchange 2000 the message transfer agent, or MTA, in Exchange was based upon X.400 and RPCs. This technology served its purpose well and produced a very functional transport core for companies implementing Exchange 4.0 through 5.5. An obvious question is why would Microsoft change something that is working very well? The answer can be found in the underlying operating system, Windows 2000.

With Windows 2000, Microsoft has exposed and relies heavily upon the Active Directory. Directory services, and especially the Active Directory, bring many benefits to an enterprise. One technical benefit and capability of the Active Directory is the integration of DNS. The other obvious benefits the Active Directory brings...