ServersThe Zimbra Challenge

The Zimbra Challenge

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Zimbra Collaboration Suite Network Edition: Open source, standards-based e-mail and collaboration server that also integrates several important open source products.

Does the open source, standards-based e-mail and collaboration server live up to the hype built around it? Does it have what it takes to be the Linux alternative to Exchange?

In these heady days of burgeoning communications opportunities, to be ‘just an e-mail server’ is considered passe in some circles. The majority of mail server are now designed to include instant messaging, VoIP, RSS, or groupware/collaboration features. Zimbra Collaboration Server (ZCS) is one of the best of the new lot, built with multiple communication features in mind, using open source programming and focusing on accepted standards. Although it went through a lengthy (more than a year) beta process and was finally released in early 2006, Zimbra is still a work in progress.

Being a ‘work in process’ is normal for open source software, and in no way is it pejorative. In this context, it does indicate Zimbra is still a maturing product, not only is its feature set evolving, but its fundamentals are still being improved and polished.

In this context, it does indicate Zimbra is still a maturing product, not only is its feature set evolving, but its fundamentals are still being improved and polished.

Zimbra is currently offered in two editions: Open Source Edition (free) and Network Edition. The Network Edition has two version, Standard (500+ users at $28 per user) and Small Business ($1,450 per 50 users).

To move customers from the Open Source Edition to the Network Edition (and thus bring in revenue), Zimbra spices the dish with Microsoft Outlook (MAPI) connectivity, attachment indexing and search, attachment rendering in HTML, online backup/restore, hierarchical storage management, cluster support, delegated administration, and additional product support. Many of these features are relevant at the enterprise level but not the small business level.

We sense, not surprisingly, in the range of packaging and pricing that the marketing focus of Zimbra is unsettled.

Swift installation is helped by a consolidated script that adjusts components for supported platforms. Recommended hardware, which should be taken seriously, is fairly robust: a 2 GHz CPU, 2 GB of RAM, a minimum of 10 GB of storage for operation and ‘plenty’ of storage space for messages, ideally in a RAID configuration. Zimbra also supports hierarchical storage management.

Building Server Muscle

The Zimbra collaboration server is itself an interesting collaboration. It ships with and uses several major open source products: Postfix for the mail server, Apache Jakarta Tomcat application server to power most of the programming, MySQL for metadata management, Apache Lucene search engine for message text, and OpenLDAP for directory (LDAP) management. Zimbra binds these components together with its own (open source) Java programming to provide the e-mail server, calendar server, and contacts server. In doing this, it adheres closely to contemporary standards, such as POP3, SMTP, IMAP, SOAP, and XML, so it can easily work with products like Microsoft Outlook and Microsoft Exchange Server.

In developing the server components Zimbra made some design choices worth highlighting: Messages are stored in MIME format, and only one copy of a message is stored, regardless of how many recipients (on that same server). Each Zimbra server has its own message, data, and index store for the mailboxes on that server. To scale up (more mailboxes), simply add more servers — thus it offers horizontal scalability. Zimbra uses the MySQL database manager to store a large amount of data about messages, users, threads, and similar information (i.e., metadata).

For enterprise-level scaling, the standard network edition relies on the capabilities of the Red Hat Cluster Suite and recommends Postfix be run in its own server for best performance. Although Zimbra has been designed with higher-end performance in mind, the diversity of third-party components may complicate the path. The components are not highly visible in routine use; however, in our testing we found in-depth knowledge of individual pieces (especially Postfix and Apache Tomcat) may be necessary for troubleshooting and maintenance.

Holding all the elements together requires two approaches, a browser-based administration console and command-line management. The dual interface and its many small presentation problems are indicative of a user interface that needs work. Such enhancement are, in fact, part of the scheduled upgrading of the product. Remember, Zimbra is a work in progress.

Users and Security

Management of users and system security (the two go together) is functional and reasonably well-handled in the administrative console and utilities. There is, however, a bit of jumping around to accomplish some tasks. For example, there is a wizard to enter individual accounts and a command-line utility for loading new accounts in bulk (from a text file). Zimbra uses OpenLDAP to connect with external directory services for user identification and authentication. A utility program to transfer users from Microsoft Exchange Server is also available.

Like most e-mail servers, Zimbra provides many ways to manage and regulate user accounts. This can be done individually, or by defining a ‘class of service’ (COS) ׫ a group to which accounts belong. Each class may have rules and properties assigned to it, which apply to each member account.

To protect the server (and its users) from the ever-present dangers of viruses, spam, and nefarious e-mail relay, Zimbra turns to a battery of open source software that plugs into the Postfix server: SpamAssassin for spam catching, ClamAV for anti-virus, and Amavisd-New, a Postfix content filter. Together with its own user-control, relay management, and event logging, Zimbra provides good mail protection.

A Client With the Strength of AJAX

Although it supports client email programs such as Microsoft Outlook, Zimbra garners most attention for its own Webmail client. Only with the Zimbra client does the user get the nifty ability to ‘mouse over’ names in messages and see a bubble display of contact information, or mouse over a date and see a schedule for that day. These and other user interface filigree distinguish the Zimbra client. It has also attracted attention because it is a fine representative of an important and trendy approach to programming Web software, the so-called AJAX (Asynchronous JavaScript and XML) technology that has been identified as part of the ‘Web 2.0’ movement.

Whatever the approach, from the user’s point of view, the Zimbra mail client provides a snappy interface. It is well designed, supports useful calendar and contact management, and is flexible enough to involve other forms of communication, such as RSS and VoIP. Messages are fully indexed. There is a spell-checker (Aspell, another open source item). However, it does not cover the full range of functionality in Microsoft Outlook (no tasks, notes, or journaling), nor does it have the breadth of user customization.

Zimlet Eyes

Extensibility is one of Zimbra’s assets. This flows from its open source, standards-based approach. It also reflects a concerted effort to provide easier ways for developers to modify Zimbra functionality. Chiefly, this is delivered in two parts: the Zimbra AJAX toolkit, a bundle of useful programming tools, and ‘zimlets.’ Zimlets are pieces of programming (objects) designed to connect Zimbra with external services. For example, it can serve as a gateway to extend the basic e-mail into new areas of communication, such as VoIP and RSS. Current zimlets support Yahoo Maps,, Wikipedia, and other services.

Zimbra leans heavily on the open source “pedigree” to position itself against the competition. Certainly, with regard to customization, it is a strength, as is the use of AJAX for developing the client. Longer term, juggling versions of several open source products may be a headache, and Zimbra will need to show that stitching them together doesn’t impair performance. So far, it has done an admirable job of combining everything into a surprisingly well-operating whole.

Pros: Good standards support; Open source version; Innovative e-mail client.
Cons: Limited mail list management; Does not run on Windows servers.

Reviewed by: Nelson King
Original Review Date: 3/29/2006
Original Review Version: 3.0.1

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