Our civilization demands that I be profitable to a parasite who leeches a majority of my labour’s value in order to accumulate obscene levels of wealth.
Without exorbitant amounts of time spent maintaining that profitability, I will end up poor, homeless, and eventually dead from exposure. This leaves vanishingly little time to spend on open source work, regardless of how intellectually and ethically attractive it may be.
Thunderbird is acquiring Exchange features.
They haven’t turned them on just yet owing to a little last-minute work, but your ability to sync calendars and address books with an ActiveSync/Exchange-compatible eMail server is coming soon.