Open-Xchange (OX for short) promotes itself as the “leading solution” in the open source email and groupware market. Whether or not that’s true is open to debate, but it is an established solution with, as well as an enterprise server (Open-Xchange Server Edition) a more scalable and modular implementation for service providers (Open-Xchange Hosting Edition). Both are commercially licensed and the bulk of the product is open source.
The core OX server is written in Java, run as an independent service on Linux with support for Debian, plus Red Hat and SUSE Enterprise platforms. A number of other common open source components are also utilised including MySQL to handle the data store, Apache for client communication (using HTTP/S) and a choice of either Dovecot, Cyrus or Courier IMAP servers although, according to the developers any SMTP/IMAP service can be incorporated.
At the user end there’s a custom AJAX based browser client with the usual Outlook-like GUI that supports all the messaging and groupware features. Alternatively there’s an Outlook plug-in referred to as the Outlook OXtender (open source humour!), but only for use with Outlook 2003/2007. Earlier versions are not supported.
The OXtender, is neither free nor open source and, unlike plug-ins for most other Exchange clones, isn’t involved in message handling. It just looks after the groupware features, synchronizing the contents of local calendars, contacts and tasks folders with data on the OX server. Journals and Notes aren’t supported in the current version, although folder sharing is, along with a global address book and both personal and group calendars. Automatic checking of free/busy time is also available when scheduling calendar events through Outlook.
Synchronisation of the groupware folders is done using what’s called OXDAV, effectively XML structures transferred using WebDAV, with a triggered push mechanism and server-side caching to minimise the amount of client/server traffic.
Email messages, meanwhile, are sent and received using the native Outlook SMTP/IMAP/POP3 account facilities, with IMAP strongly recommended over POP3. Unfortunately that means users don’t get a single integrated Inbox, just the usual Personal Folders Inbox and another for each IMAP account. Moreover, because it’s pure IMAP, there’s no immediate notification when messages are received and deleted messages have to be purged before they’re removed from the server. That’s quite different from the Exchange experience and something of a drawback for buyers looking for an open source replacement.