My boss wants us to setup an internal email, task, and calendaring solution for our company. We had previously used our ISP for email services. We are very close to going with Microsoft Exchange, but I would like to know what my options are on the Linux (and in particular, SuSE) side? Are there good open-source and/or commercial options that have great security and collaboration features? Someone at our company heard some guy talking about how he has an email, task, and calendaring solution running on Debian, but he didn't get details. I'm also curious .. how do these options compare to MS Exchange in terms of administration? We already paid for a copy of Exchange, but if anoter solution is easier to administer and more secure, we'll go with it. Thanks for the advice!