In terms of managing IMAP connections, async is definitely the way to go. For our product, lightermail.com, I ported Python's imaplib to run on Tornado's ioloop (adding a few features like IDLE support and command pipelining). Not only can you manage a lot of connections with little memory, but you can do some really cool things (like the pipelining of commands mentioned above) that are unavailable to regular synchronous IMAP clients. Plan to open source the implementation when I have a bit more time.