C.3. Open Source Email Server SolutionsOpen source solutions in the email server space tend to comprise combinations of open source projects. This is because comprehensive solutions such as Microsoft Exchange and Novell GroupWise have set the expectation of a single email system that takes care of all the enterprise's email serving needs, or at least those of a department within an enterprise. The open source community's answer to this challenge is to combine several open source projects that work well together. Open source email server software provides a low-overhead way to manage large volumes of mail. With appropriate staff expertise, open source-based email server solutions can also reduce an IT group's exposure to the perils of spam and viruses. C.3.1. Open Source Email Server CapabilitiesIt is instructive to look at Microsoft Exchange's capabilities, because Microsoft Exchange offers a feature set that meets most of an enterprise's common email requirements. We purposefully underemphasize collaboration features here since we address collaboration as a separate topic in Appendix D. Here is Microsoft Exchange's feature set:
In addition to these features, an enterprise-grade email server should also have the following capabilities:
C.3.2. Open Source Email Server ProjectsWe define open source email servers as a combination of Mail Transfer Agents (MTAs) and Mail Delivery Agents (MDAs). An MTA is a program responsible for transferring a mail message. When an MTA receives mail from a Mail User Agent (MUA) or another MTA, it stores it locally on a temporary basis and analyzes its recipients. The MTA either delivers the message by handing it to an MDA or passes it on to another MTA. An MDA is a program that delivers the message by storing it in the recipient's mailbox. Open source email server projects have been greatly improved and are more commonly used in enterprises. Open source email server software provides a low-overhead way to manage large volumes of email. With appropriate staff expertise, open source-based email server solutions reduce the exposure of an IT group to the perils of spam and viruses. The field of open source email servers has a long and rich history. Since email was the first mass application on the Internet and it continues to be the most popular one today, the email server field is rich with mature choices. Sendmail was the first major email server and, at one point, had 80% or more of the market shareor so goes the folklore. However, Sendmail was designed and built to requirements that are obsolete today. What's more, it wasn't designed to scale on management, security, or performance fronts. Most current open source email server projects support common mailbox formats and provide various levels of integration. The key to easy adoption and effective use of open source email server projects is to identify a collection of projects that work well together. For example, using Courier-IMAP, Postfix, Clam AntiVirus, and SpamAssassin will provide a full MTA with shared folders, virus protection, and defense from spam. Some modern Linux distributions include, or make it very easy to install, these projects during installation. |