Chapter 3. Messaging Architectures

This chapter describes the architectures of some of the more common configurations and explains that there are almost infinite combinations. It outlines the pros and cons of each architecture to provide you with information to determine which architectures meet your enterprise messaging requirements. Chapter 10, “Security,” on page 153,” addresses security in detail, but a secure architecture is discussed in this chapter to indicate the use of firewalls in multiple layers, that is, a demilitarized zone (DMZ) as not all messaging systems actually are behind firewalls.

This chapter covers the following topics:

• Directory

• MTA

• Mailstore

• Proxy Servers

• Simple Single-Layer Architecture

• Simple—Alternative Architecture

• Typical Architecture

• Secure—Basic Architecture

• High Availability—Failover Architecture

Often there is more than one method of doing things. Designing and installing a messaging system is no different. Depending upon your organization's specific goals, skills, and networking environment, one architecture may be more relevant than another.

Generally, the architectures can be organized into several categories or combinations of categories:

• Simple Single Layer

• Multitiered

• Secure

• Highly available

To help you understand more about messaging architecture, this chapter reviews some of the basic parts of the messaging system first.

Four basic parts of a messaging system are important or can be sized.

• Directory

• Gateway, also called message transfer agent (MTA)

• Mail server, also called mailstore

• Proxy server