I just noticed that there is now a Ruby-based IMAP server available. Ximapd is only at version 0.0.4, which suggests that it isn’t exactly production-ready, but I’ll be following it as it develops over the next few months. Like the Ruby WebDAV server that I talked about a month ago, the big value in these sorts of servers is the fantastic things that you can do when you integrate them into non-traditional contexts. For example, a workflow system that can give a web view of the documents that it manages, while also acting like a file server and an email server. Changes to files or email messages are interpreted as actions in the workflow system and then the system state changes appropriately. That lets the users manipulate the data in the system in natural ways using familiar tools.
Another idea: nn email-support ticket system that only shows internal users the mail associated with open tickets that they own. When the ticket is closed, the mail goes away on its own.