Due to our enterprise licensing agreement, our employees can get Office from MS at a massive discount. If I didn't have the full Outlook client on the cheap, I don't know what I'd use. I'd probably start with another look at T-bird, even if the development has stopped. I don't know about using an e-mail based exclusively on the web.. Something about it makes me uncomfortable, but then so do many other web-based tools for managing personal or private information.