Scalix plans to open the source for their Community Edition. When I was at HP (for 14 years!), we thought it would be impossible to open source OpenMail. The code was thought too polluted with stuff that we didn't have the rights to publish. Things like dbVista and the Microsoft-proprietary TNEF unpacker.
Looks like the ex-OpenMail engineers at Scalix Bracknell have some Interesting Times ahead.
However, it looks like the opened code won't include the MAPI Outlook bits. By specifying the "Community Edition" Scalix is signaling that it won't publish the source of things like MAPI, TNEF, AD integration, and Ajax group scheduling.