Ever since version 2.0, the iPhone OS has supported push notifications for Microsoft Exchange-based e-mail accounts. This is an efficient and convenient feature for people who have such an e-mail account, but let's face it - unless you work in a high-end corporate setting, you probably don't have one.
However, IMAP e-mail accounts are much more readily available from services like Gmail, AOL, Fastmail, and others, and it turns out that the IMAP protocol supports a form of push notifications too. This would be great news for all the IMAP users with iPhones who want push notification - except that the iPhone OS doesn't support that type of push.
At last, this gap has been bridged. iPhone users can finally get real-time notification of new emails sent to their IMAP accounts thanks to msgpush.com, an easy-to-use solution launching in beta today. The company is releasing a limited number of accounts, available at www.msgpush.com, to coincide with the Apple Worldwide Developers Conference 2009.
The service is free (for now), and I can confirm that it actually works and is pretty easy to set up. Neat!