I was looking for a mail server for Windows with IMAP v4 support, to use in a project. I came across and installed Axigen. The free version allows 100 accounts, good enough for my needs. They require you to register, and send a license key that is good for a year. The setup was painless. The admin interface is browser based. Setting up IMAP with SSL was straightforward. I needed SSL to use plain authentication using the login command of IMAP. They also have a version for Linux.