Section C.3. Open Source Email Server Solutions


C.3. Open Source Email Server Solutions

Open 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 Capabilities

It 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:

  • Full support for major email protocols like SMTP, POP3, IMAP, and WebDAV

  • Active Directory integration with full support for global address lists across the enterprise

  • Outlook web access and a full-featured web mail client, with S/MIME support, desktop-application-style shortcuts, task lists, and an integrated spellchecker

  • Deep integration with Outlook 2003

  • Security features such as S/MIME and HTTPS support, attachments, and complex HTML blocks that prevent propagation of viruses and malware attacks

  • Advanced collaboration features such as public folders and shared calendars

  • Support of clustered implementation for larger deployments across multiple locations

  • Integrated support for mobile devices via Outlook Mobile Access, with support for related industry standards such as WAP 2.x, i-Mode (XHTML), and Compressed HTML (cHTML)

In addition to these features, an enterprise-grade email server should also have the following capabilities:


Advanced relay support

Advanced email servers are expected to distinguish legitimate email that originated from one of its end users and relay only that email. With some newer protocols, such as "pop-before," an email server relays outgoing email only from users who are currently actively receiving email via its POP server. With "smtp-auth," the email reader provides a username and password when sending email.


Administration features

These include mailbox quota-control support, as well as Webmin support for web-based administration.


Sendmail compatibility

Because of Sendmail's past dominance, many supporting programs and scripts assume the presence of Sendmail. As a result, most email servers aiming to replace Sendmail provide mechanisms so that the replacement is transparent to these supporting programs and scripts. Sendmail compatibility remains a key criterion for an email server to be a serious candidate for consideration in the enterprise.


Mailbox format support

This includes support for mbox and maildir. mbox is the traditional Unix mailbox format in which all messages are stored in one file and indexes are built to locate messages efficiently. maildir, on the other hand, uses the Unix filesystem to store one message per file. The maildir format was designed to avoid locking and to address other performance issues encountered by the mbox format in high-volume email scenarios.


Support for RDBMS

Newer email servers are experimenting with using a database to store messages, thus leveraging database technology for higher concurrency and reliability needs.


Content scanner support

This is the ability to hand a message's contents off to a content scanner (such as SpamAssassin or Clam AntiVirus) for analysis and custom actions such as flagging the message as spam or quarantining it based on its analysis.


Security and encryption

This is the ability to accept encrypted connections from email readers and provide the end user with a fully secure email experience.


Back-end support

The ability to verify senders or recipients with external directories, including LDAP-based directories or Active Directory-based directories, is vital.


Virtual host support

This is the ability to receive and send email on behalf of more than one domain.

C.3.2. Open Source Email Server Projects

We 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.



Open Source for the Enterprise
Open Source for the Enterprise
ISBN: 596101198
EAN: N/A
Year: 2003
Pages: 134

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