Citadel, (http://www.citadel.org) -- A lot of features, but the UI is somewhat dated. It would be interesting to see a revival.
OpenXchange, (https://www.open-xchange.com) -- Commercial project with an open source core. Much nicer UI, I'd be worried about long term support if/when the original company stops developing it.
Citadel, (http://www.citadel.org) -- A lot of features, but the UI is somewhat dated. It would be interesting to see a revival.
OpenXchange, (https://www.open-xchange.com) -- Commercial project with an open source core. Much nicer UI, I'd be worried about long term support if/when the original company stops developing it.