Outlook Exchange Server to Open Source Alternatives?

[Mike McMullen]

Hi All,

As part of a larger project to move our company away from Microsoft
products, I'm investigating options for replacing our enterprise
exchange server.

We have about 500 mailboxes that would need to ported out as well as
public folders and contacts/calendars etc.

Can anyone recommend a linux groupware solution that would enable us to
provide an Outlook like environment? And allows importing of prior data?

Thanks!

Mike