Recommendations for the Right IMAP Server?

eugene ts wong asks: "Our company is planning on taking care of its own email, by setting up our own server. I've been given the task of researching what is out there. So far, I've got my heart set on an IMAP server that we can install on Gentoo. Unfortunately, email isn't our forte, and I really have no idea of where to start. I've made some google searches, browsed around on the IMAP site, and also found this email. According to the mutt documentation, Cyrus and Courier are the best choices." What IMAP servers have you used, and which ones would you recommend?

"I'm still at a loss for what to do. The documentation of all but uw-imap seem to be a bit complex for me. If it helps, I'd like to point out that I have Mutt and nbsmtp installed, which work fine for connecting to our SMTP and POP servers. How do I know what will serve our needs the best? Also, is there an IMAP server that I could install easily for testing and learning purposes? I'd like to be able to get something installed without much configuration. Security shouldn't be an issue for testing purposes, because it will only be on the local network, and the computer will be turned off when I'm not actively testing it. We're also willing to purchase products as well. We're willing to hire a professional to do it for us, but the boss wanted some research done so that we know what we're getting. Any comments are welcome. Thanks in advance."