We've been using communigate for about a year and a half now at my company (replaced all our windows+exchange servers with centOS+communigate), and I must say it's been a great alternative to exchange. It's got all the features you need and a pretty good web interface. Their info is at
http://www.communigate.com/
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We've been using communigate for about a year and a half now at my company (replaced all our windows+exchange servers with centOS+communigate), and I must say it's been a great alternative to exchange. It's got all the features you need and a pretty good web interface. Their info is at http://www.communigate.com/