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This chapter is from the book

Messaging and Collaboration

Technically, messaging and collaboration could be included in the previous section with enterprise applications because it's almost always mission-critical and is used by every person in an organization. Mail is such a significant application that it merits covering it separately, looking at what is available, how it can be implemented, and some strategies for coexistence with other mail systems because this is often a common problem for enterprise companies.

It can be argued that email, not the web server, is the killer application for the Internet. More than half the people in the United States use email, and that's a low percentage compared to some other parts of the world. The point is, a lot of people use email and a lot of it is business related. For that reason, email becomes a critical part of not only a company's internal operations, but also a company's outward face to the world. If email goes down, internally production grinds to a halt. Externally, you lose contact, presence, and, ultimately, business.

Everything about Linux discussed to this point as far as security, reliability, performance, and scalability, therefore applies to email as much as any other application. Fortunately, email capabilities and solutions have evolved along with the Internet from the very beginning, so several viable options are available from which to choose. Novell believes that some messaging and collaboration options are better than others, but when it comes to open source, the customer should decide. Open source messaging solutions include Postfix and Sendmail. A number of commercial email packages are also available on Linux, but Novell GroupWise is highly recommended.


Before describing what solutions are available, it's worth taking a little time to outline email architecture. Email solutions generally are not a single application package on a single machine, but are a distributed collection of interconnected services that require multiple elements to get mail from one point to another. This distributed nature provides some flexibility when considering how to deploy or implement email. The common elements of a mail solution include the following:

  • SMTP message transfer agents—These include Simple Mail Transfer Protocol (SMTP) agents, agents that act as mail carriers, transferring mail from one location to another. These processes are responsible for directing outgoing mail to other SMTP agents in other locations. They are also responsible for directing incoming mail from other locations to a local POP or IMAP server.

  • POP/IMAP message transfer agents—Post Office Protocol (POP) and Internet Message Access Protocol (IMAP) agents transfer mail in user-specific message stores (sometimes called post offices) to individual user clients. POP and IMAP function slightly differently in that with POP, all messages are moved from the message store to the message client. With IMAP, messages can be retained at the message store for access and manipulation.

  • DNS—Domain name servers act as local or Internet-wide lookup tables for SMTP agents. Using DNS, sending SMTP agents can determine the correct IP address of the receiving SMTP agent based on the domain name of the email address.

  • LDAP—Lightweight Directory Access Protocol (LDAP) directories are often used as a control list, authorizing access to message transfer agents (MTAs). LDAP directories are also used as email white pages to look up email addresses for individuals.

  • Email clients—Client applications interact with POP/IMAP message transfer agents (or servers as they are often called) to send, retrieve, and organize email and email attachments.

  • Web access—A common mail requirement is the capability to access email from any location without a mail client. This is made possible using a combination of web server and web-based mail access services.

  • Mail protection—Critical to productivity and mail security is the ability to protect against viruses and filter spam. This can include dynamic virus or spam recognition filters with scanning and deletion policies.

Several viable open source email solutions are available, as well as many commercial email applications that are standards-compliant. The leading open source solutions are viable for enterprise organizations, depending on the level of features needed. Most Internet service providers (ISPs) use open source mail solutions providing client-based and web-based access to email for thousands and thousands of users. With proper scalability load balancing techniques, these solutions scale well and adequately provide basic email services.

The most common open source email solutions consist of one or more of the following components:

  • Sendmail—Sendmail is a popular open source message transfer agent available for Unix and Linux systems. Sendmail originated at UC Berkeley in the 1980s as a rewrite of the ARPANET delivermail program, the first mail service for the Internet. Sendmail is estimated to be running over 40% of the mail servers on the Internet, so it has functionality that is useful to a large population. Sendmail critics claim it is insecure, difficult to manage, and slow. Sendmail includes both SMTP and POP/IMAP transfer agents.

  • Postfix—Postfix was developed as a fast, easy-to-administer, secure alternative to Sendmail. It was originally developed at the IBM T.J. Watson Research facility as Vmailer and IBM Secure Mailer. It doesn't send mail from the root user, can reload settings without being downed, and can use a standard database to store configuration information. Postfix also includes SMTP and POP/IMAP transfer agents.

  • Mail clients—Several popular open source mail clients work with Sendmail or Postfix. The Mozilla (Netscape Communicator) mail components have been enhanced in new Mozilla versions Thunderbird and Firefox. LinuxLinks.com "Mail Clients" section includes entries for 117 different open source clients. Common Windows-based email clients that work with standards-compliant POP mail servers include Microsoft Outlook, Pegasus Mail, and Eudora Email. You can use any of these standards-compliant browsers with Postfix or Sendmail as well as POP/SMTP-compliant mail servers such as GroupWise.

  • Directory server—Like mail clients, there are open source versions of LDAP directory server, and there are proprietary or commercial versions as well. Because LDAP is an open standard, mail clients and mail servers can use any standards-compliant LDAP server for authentication and lookup. The most common open source LDAP directory is OpenLDAP, a server implementation of LDAP that includes the LDAP daemon and the tools and utilities for implementing client applications. LDAP Java class libraries are part of this project and were contributed by Novell. Novell has included LDAP compliance and a host of LDAP-based solutions as part of eDirectory. In addition to other services, eDirectory functions as an LDAP directory for mail server and client applications.

Novell GroupWise

For many organizations, basic email using a POP client and SMTP server is entirely adequate. Mail with attachments is the only required form of collaboration, and using standard hardware and software platforms, the mail always gets through.

If you want a richer feature set, however, it's available. For years, Novell has offered the premier communication and collaboration solution GroupWise. GroupWise includes several features not available with standard open source solutions that are often highly valuable to organizations. The short list includes calendaring, scheduling, busy searches, message retraction, document management, rules-based message handling, shared folders, message routing, and much, much more. Using GroupWise Web Access or Evolution, these features are available through a browser client.

Collaboration is one area in which open source has not provided a substitute with equivalent features, and Novell's product offering is an excellent complement. Novell GroupWise runs on Linux as well as NetWare and Windows. Advantages of GroupWise on Linux include flexibility, scalability, and security. The GroupWise architecture expands to include post offices, server-based mail repositories that house user mail and content. These can be strategically positioned on different servers for performance gains and in different locations for quicker access by users. The distributed, modular nature of GroupWise makes it possible to easily scale so that thousands of users in multiple time zones can have easy access to rich planning, calendaring, and collaboration tools—all while providing failover and redundant systems for uninterrupted services.


Email integration, especially with company mergers and acquisitions, has historically been a nightmare. Before email transport protocols and message formats were standardized, practically all major mail systems were proprietary and could only be merged with the use of sophisticated and customized integration solutions. Today, using Linux and open source as a framework or interim step in email migration or deployment can deliver significant advantages.

Because email is a typical client/server application, moving the server to Linux is a process that can be done with very little impact on end users. Because standards-based POP/IMAP mail is a simple text format, mailboxes can be migrated with very little effort. Most email clients have import utilities that allow you to pull mail from other client formats with a couple of simple commands. With Linux scalability and performance, consolidating email servers or services can simplify administration and reduce management costs.

Using LDAP directories instead of proprietary mail user lists in conjunction with other applications or services that are user-based can also simplify management. A single directory, instead of multiple (often out of sync) user lists provides the advantage of one-stop change management.

Novell simplifies the process of consolidating/migrating both directory and email. The GroupWise migration utilities allow you to easily convert from Microsoft formats to GroupWise, while the Import Conversion Export utility enables administrators to move date between LDAP directories or import directory information to Novell eDirectory.

Email needs vary from organization to organization and even from group to group within organizations. Between open source options and Novell's GroupWise offering, an entire range of email selections is available—simple email to full-blown collaboration. Clients can be web-based, open source, or full-featured desktop for Windows, Macintosh, or Linux. Novell supports all levels of an open stack email solution.

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