I've become a bit obsessed with getting the mail client on the iPhone working in a more reliable manner and have now become convinced that the much-heralded Yahoo! "push" implementation which Jobs trumpted during his keynote is not actually a true "push" service at all (i.e. it doesn't use IMAP IDLE and apparently doesn't use P-IMAP as some have asserted here). Rather, I believe that the system which is actually in place is something similar to AUTD -- the quasi-push implementation utilized on pre-WM5 devices. My reasoning is based upon the following observation: Whenever you perform a manual e-mail pull on the iPhone, it automatically pulls mail from ALL mail accounts which the user has created on the device. Currently, I have two accounts set up on my device: Yahoo! and Fastmail. I set the device to check for mail "manually" which is supposedly the correct setting for Yahoo! "push" and which, theoretically, should keep my Fastmail account dormant unless and until I do a manual sync of that account. However, what actually occurs when a new Yahoo! "push" message appears is that I also get any new messages which have been sent to my Fastmail account at the same time. Thus, it would appear that the receipt of a new message in the Yahoo! account triggers the phone (likely with a hidden SMS message) to perform a manual pull on the device, thereby pulling from all accounts. This might explain why Yahoo! push is so damn buggy (I always hated AUTD and found it completely unreliable). Any thoughts? Edit: Apparently, the fine folks over at Fastmail (say that ten times quickly) have come to the same conclusion. See http://www.fastmail.fm/docs/forum/index.html This is very disheartening.