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Open source Exchange replacements

The H takes a look at four open source alternatives to Microsoft Exchange Server for messaging and groupware

by Alan Stevens

The messaging and groupware landscape has altered significantly in the last few years with, like it or loathe it, Microsoft’s Exchange Server now firmly ensconced as the number one solution regardless of customer size or industry sector. There are alternatives, of course, but rival developers have more or less given up on trying to beat Microsoft at (what’s now) it’s own game. Instead most now concentrate their efforts on developing alternative messaging and collaboration servers which to end users, and their applications, look and behave just like the Exchange they’re hoping to replace.

The marketing issues

Given Microsoft’s stranglehold on the market, changing tack this way makes good sense, but isn’t as easy as it might sound. How, for example, do you get customers to buy into what appears to be little more than an Exchange clone, when the original is widely used and so well supported both by Microsoft and developers of third party apps?

A number of approaches have been tried, the most common being to first undercut the Microsoft server on price, often by huge amounts, at the same time emphasising how much easier the alternatives are to configure and manage. Many of the alternatives are also open source, able to leverage well established message transfer, database and other components, thus making it easier for developers to integrate other applications and add extra features. Moreover, the majority are written to run on open source Linux, bolstering the cost reduction arguments and, at the same time, addressing a lot of the security and support issues associated with a proprietary product like Exchange.

However it’s not just server buyers and system administrators who need to be convinced. Email is the number one killer application and if users don’t like what they’re given it can have a major impact on productivity. Nine out of ten will be Outlook users and will resist any move to make them switch to anything else. Even to browser-based implementations such as Outlook Web Access in Exchange, which can be made to look very similar, but not completely the same.

To win users over, therefore, any Exchange replacement, has to not just work with Outlook, but must deliver exactly the same functionality in exactly the same way as if connected to a Microsoft host. That means being able to do a lot more than just send and receive emails. It means being able to lookup recipients in a common, global, address book, share folders with other users, delegate and, critically, share calendar information. The ability to push message notifications out to the client as soon as emails are received is another key requirement, along with off-line working plus synchronisation with mobile devices such as Windows Mobile smart phones and BlackBerry.

The technical issues

Setting the goals is hard enough, reverse engineering a complex product like Exchange Server even harder. All the more so given the tight binding of the Outlook client to the Exchange server. OK, support for standard protocols such as POP3 and IMAP means that Outlook can also work with other SMTP solutions, but it delivers most of its functionality by leveraging Exchange server features, exposed to the client via Microsoft’s Messaging API (MAPI).

There’s no way of getting around this association other than by adding some kind of MAPI emulation to the mix, with a number of ways of going about it. The most common is an Outlook plug-in, able to speak MAPI to the Outlook client, then translate those conversations into whatever protocols and APIs are used on the host server. Another is to go for server-side MAPI to enable the client to speak directly to the server using the same API as Exchange, although most implementations to date still require an Outlook plug-in to handle the communication protocols employed. Plus there are few who mix these and proprietary techniques such as off-line synchronisation of IMAP folders to mimic some of what Exchange can do.

Just how successful such workarounds are at mimicking the Exchange experience can vary considerably. What follows, therefore, is an overview of what to expect from the four leading open source products – Open-Xchange, Scalix, Zimbra and Zarafa, all of which claim to have a high degree of MAPI/Outlook support.

Note that the emphasis is on Outlook and Exchange interoperability, so details of other features will, necessarily, be brief. However, it’s important to appreciate that these products have a lot more to offer beyond what we’re looking at, with lots of information regarding other features to be found on the product websites.

Next: Open-Xchange

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