Zimbra Collaboration Server: Open source messaging server for Linux/Mac with enterprise collaboration. It's been more than a year since Yahoo! bought the open source mail server company Zimbra, and people are still talking about the technology. We put the most recent version through the paces.

In the server software marketplace, open source software and commercial software often appeal to and target different customers. Typically, enterprise-oriented servers are built around closed-source commercial software, while open source software is marketed toward enthusiast-driven organizations or smaller businesses with a strong interest in cost cutting. In the messaging server segment, Microsoft Exchange has become something of a de facto standard, and it, like many of its competitors, sells traditional closed-source solutions.

Zimbra Collaboration Server (ZCS) separates itself from the pack in several ways. First and foremost, it occupies a newly emerging niche of "commercial open source" products. That is, the base version of ZCS is open source software, free to acquire or modify.

Zimbra recently passed the first anniversary of being acquired by Yahoo! By most measures, the acquisition has been a success. The mail technology is being integrated in both directions, and Zimbra's client base has grown steadily, John Robb, vice president of marketing and product management, told ServerWatch.

ZCS, therefore, is more than just open source. Licensed versions offer additional functionality above and beyond the open source version are also available. These may appeal to customers with particular messaging needs. Plus, ZCS runs primarily on Linux-based platforms, although it is also available for Mac OS X. There is not a Windows version, but the server can certainly interoperate with clients on Windows platforms. An open extension framework is also available that enables two-way interoperability with leading collaboration platforms, including Microsoft Exchange Server, Lotus Domino Messaging Server and Meeting Maker.

Installing the 350MB ZCS download requires administrator access and some familiarity with using the command-line. You may need to install additional system libraries for the ZCS installation script to pass its preliminary checks. You will also need to configure your hosts file with accurate FQDN syntax. Although it is accurate to describe ZCS as an open source messaging server, it is even more accurate to describe it as a bundled suite of open source products, including Apache Tomcat, MySQL, Lucene and Postfix.

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Zimbra has already done the heavy lifting of stringing together these disparate open source products into one integrated bundle. The installer script sets up each module, and it offers to configure some optional components, such as archiving and discovery services, which require a separate license to enable. ZCS is administered through its AJAX-based Web interface. Navigating the administration menus is straightforward, helped by a clear layout and built-in "help desk" resources.

Like most collaboration servers, ZCS provides users with e-mail, contacts, calendaring, tasks and shared document storage. Each component features strong functionality. For example, e-mail includes full searching and tagging; calendars include free/busy management, users can host multiple calendars, and subscribe to external calendar feeds; and documents can be composed in place with rich editing tools and shared privately or published to a public URL.

The open source ClamAV anti-virus kit is integrated into ZCS, so there is no third-party subscription needed to keep your virus database up-to-date. However, you can optionally employ third-party commercial scanners. Consistent with its open source pedigree, SpamAssassin is the anti-spam defense of choice. Although both ClamAV and SpamAssassin are well regarded defenses and commonly found even in commercial products, some commercial servers do offer a wider range of additional defenses, particularly against spam. The Linux version of ZCS offers an additional form of security for attachments by rendering certain file formats, like Word documents, in HTML inside the message pane rather than requiring the user to launch a separate application.

In addition to the usual collaboration tools, ZCS offers a novel feature called the "zimlet." The Zimlet architecture enables developers to integrate third-party products with Zimbra, somewhat like "gadgets" in OS X or widgets in Windows. Several zimlets are includes with ZCS, such as Yahoo! Maps, which can display a contact's address on a map, and the Flickr zimlet, which simplifies attaching photos from a Flickr account to a new message.

For end users, the ZCS server is reachable with any standard e-mail client. To take advantage of collaboration features the best choices are either Outlook on the desktop or Zimbra's own Web-based client. To its credit, Zimbra has designed an AJAX-based Web client which is nearly as full-featured as a desktop client, with drag and drop and right-click support. For users with lesser connectivity, one click lets you switch to a standard HTML client, and even a mobile friendly client.

Support for push-style mobile e-mail to devices like smartphones requires licensing a separate product, Zimbra Mobile, which can interact with Java-based smartphones, plus the iPhone, Windows-based phones, Symbian-based phones, and Blackberries.

Mobility features require a license for either the Standard or Professional edition. Likewise, you will need a licensed edition to support enterprise features like clustering and product rebranding. Only the Professional edition supports syncing to Outlook and Apple iSync.

Although Zimbra is entirely functional as a turnkey collaboration server, its real appeal lies in its open source foundation and the opportunity for developers to customize a Zimbra platform precisely to their organization's needs.

Pros: Open source foundation; High-volume handling; excellent AJAX Web client.

Cons: Not quite plug-and-play for the novice administrator; Could use more anti-spam defenses; No Windows version.

Reviewed by: Aaron Weiss

Original Review Date: 10/07/2008

Original Review Version: 5.0