Many open source groupware suites lay claim to this holy grail of interoperability, but the software to synchronise address book, task and calendar information with Exchange is sold as a proprietary extension.

Speaking at the Linux.conf.au Linux and open source conference in Hobart last week, Canberra-based OpenChange and developer Brad Hards said the ultimate goal of the project is to implement the Microsoft Exchange protocols as used by Outlook, not IMAP or WebDAV, but the Exchange MAPI/RPC protocol.

"We're working with the Microsoft Exchange protocols and work it mostly does," Hards said. "Mail is easy the stuff, what is hard is the address book, calendar, free-busy lists, and notes. These are a big deal in the enterprise."

"In my workplace -- a major government department that shall remain nameless -- the main dependency on Outlook and Exchange is not mail, but seeing other people's calendars and making shared appointments. You can't get appointments with some people unless you send them invitations."

OpenChange has client and server-side libraries for Exchange integration and relies heavily on code . It is open source software licenced under the GPL version 3.