Q: How can I integrate or replace my current Microsoft Exchange setup when adding Linux to my network?

There are actually a wide variety of Exchange replacements and clients available with Linux: some offer partial Exchange feature sets, some are full solutions, and others are Linux clients that can seamlessly play nice with MS Exchange. Which one you choose depends on whether you want to simulate the Exchange functionality, provide similar functionality to Exchange, or whether you just want an alternative e-mail solution.

Exchange is made up of a number of different components, from the basic mail sending/receiving facilities of the mail transfer agent (MTA), to the e-mail boxes, shared folders, global address books, and calendaring facilities.

Exchange Simulators
Simulators enable you to use Outlook as your desktop solution while supporting the Outlook functionality at the back end on something other than Exchange. Although Exchange can provide standards-based facilities, the "power" when used with Outlook comes from custom protocols (mostly through the Messaging Application Programming Interface [MAPI]) and systems that allow Outlook and Exchange to work together more effectively. Simulators need to support this custom Outlook functionality in order to provide a true alternative to Exchange. Although it's hard to find a solution that doesn't support open standards like SMTP, IMAP, and LDAP, there are some key technologies that will allow you to use the new service with more than just Outlook.

Bynari Inc. (www.bynari.com) offers the Bynari Connector, which in turn works with Bynari Server to provide a complete e-mail and collaboration service while still allowing you to use Outlook as your e-mail client. Bynari Server, meanwhile, is a complete Linux-based solution for e-mail supporting SMTP, IMAP, and POP3 connections and using LDAP for address book functionality. Through these technologies you can start and finish your migration on both the desktop and server.

IBM (www.ibm.com) provides a vendor-supported mail server implementation. Using some of the products already mentioned, including Bynari and CommuniGate Pro, all running on an IBM zSeries Linux server, the solution can be a viable alternative to older Exchange 5.5 servers (which Microsoft is dropping at the end of 2003) and newer Exchange 2000 and Exchange 2003 products. All of this is backed up by support from one of IBM's independent service vendors.

SUSE Linux Openexchange Server (www.suse.com) provides built-in connectivity for supporting Outlook Clients to use the Openexchange services. Openexchange is based on OpenLDAP and Cyrus (an e-mail server) combined with a proprietary groupware server.

CommuniGate Pro (www.stalker.com/CommuniGatePro) supports the MAPI interface to allow Outlook to operate with the CommuniGate Pro server. The server also supports the open standards protocols for clients other than Outlook. In addition to the e-mail and collaboration features, CommuniGate Pro also includes a Web mail interface, clustering facilities, and a built-in mailing-list manager.

Exchange Equivalents
All of the previously mentioned solutions are equally suitable as an alternative e-mail server product to support Exchange-like functionality with clients other than Outlook. Sometimes, though, you don't want to continue using Outlook as a client, you just want to move lock, stock, and barrel from your existing solution to the new one. Also, if you are setting up a new ser-vice, there's no reason to even consider backwards compatibility.

Kerio's KerioMailServer5 (www.kerio.com/kms_home.html) supports most standards-based mail clients such as Mozilla, Ximian's Evolution, Mulberry, and Pine, along with Outlook in "Internet" mode. Using IMAP and general public and shared folders you can provide most of the functionality offered by Exchange. You can even create individual and shared address books that appear as a single, personalized address book for each user.

Red Hat Enterprise Linux AS (www.redhat.com/software/rhel/as) includes the software to support a range of e-mail services similar to those provided by Exchange, but based on open source software (some of which is discussed below).

OpenGroupware.org (www.opengroupware.org) is a software solution that provides a solution for the groupware parts of Exchange, such as calendaring and collaboration. You'll need to use a separate package to support your e-mail/messaging services. This solution is compatible with nearly all clients, including Mozilla, Apple's iCal, Evolution, and Outlook through a separate ZideLook plug-in.

E-Mail Software Components
Finally, provided you are willing to expend a little more time, you can use one of the many free and open source solutions, such as sendmail or postfix as your mail transfer agent (MTA), Cyrus IMAP for e-mail and collaboration, and OpenLDAP for your address book functionality.

Cyrus (http://asg.web.cmu.edu/cyrus/imapd/) is an IMAP/POP3 server that can be used in combination with sendmail, postfix, and other MTAs to provide client-based access to user e-mail accounts. It supports shared/public folders for sharing information and provides secure access (if necessary) through SASL and SSL connections.

OpenLDAP (www.openldap.org) is an open source implementation of the LDAP protocol, often used with mail services to provide login authentication and directory services for contacts, resources, and calendaring.

Going the Other Way
There is of course a solution I haven't mentioned, and that's continuing to use your Exchange Server, but in combination with Linux-based clients. You can do this by using the Ximian Connector for Exchange (www.ximian.com/products/connector/), which enables you to use the Ximian e-mail client with an Exchange server. A major advantage of this solution is that you can integrate Linux into your existing infrastructure, without limiting your Linux users, and also make the migration process easier.

Finding More
It's inevitable that we'll continue to see improvements in this particular area for Linux. As more companies use collaboration tools and Linux on the desktop increases, we're going to see more and more of the technology. You can try one of the following in a Google search box to find what is out there:

• "linux microsoft exchange"
• "linux exchange server"
• "linux e-mail collaboration"