How does Yahoo Mail push to iPhone?

Question

How is Yahoo able to send push notifications for email to iPhone/iOS in general? http://en.wikipedia.org/wiki/Push-IMAP is as far as I've gotten in my research, but I'm not sure what exactly Yahoo is doing. I'm planning to setup my own mail server and I'm curious how Yahoo is able to push but others like Gmail is not.

I should mention I'm referring to the default Mail app, not Yahoo's custom mail app (not sure if they even have one).

Thanks!

Answer 1

Yahoo's IMAP server has a special capability 'XYMAPPLEPUSHSERVICE', which presumably is a proprietary way to negotiate use of Apple Push Notification Service