This is tougher than I thought. I spend half day searching, reading, playing with demos, and it's definitely not getting easier. So I have to find out, which of the groupware apps is not changing the config of any of the core services, like postfix and courier, which is not going to be easy without fully digging in. The following suits caught my eye today:
Not so sure, if these would be suitable as well:
The main focus is on the webmail client, which should be quite advanced, being able to replace a standalone app like Evolution (the standard email client on Ubuntu), then the privat/global adressbook and calendar, a integrated bookmark feature would be nice as well. Except the bookmark management that's more or less standard for a groupware, but the quality of the webmail clients differs a lot, especially when it comes down to details like multiple personalities.
Simple Groupware and Horde offer a lot, and both are quite appealing, take that really nice view of the portal
in Horde Groupware Webmail Edition for example.
Looks like Simple Groupware and Horde Groupware Webmail Edition are on my shortlist, if they are compatible with the ISPConfig 3 setup.
Any additional comments are highly appreciated.