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Do you mean Push-IMAP? Mail.app does support Push-IMAP, or will whenever Mobile Me goes live. However it doesn't do any good if Mail.app supports Push-IMAP if the provider of your email doesn't.
 
IMAP mail is supported, has been for years and years.
IDLE is a specific feature of IMAP. It automatically notifies the client that new mail is available without requiring polling. Mail in 10.4 and earlier definitely doesn't support it natively (there are unsupported third-party plugins that do, though).
 
IDLE is a specific feature of IMAP. It automatically notifies the client that new mail is available without requiring polling. Mail in 10.4 and earlier definitely doesn't support it natively (there are unsupported third-party plugins that do, though).

It is certainly there in 10.5, and does NOT reply on MobileMe:

http://dmiessler.com/blog/hidden-leopard-features-mailapp-imap-idle-support-screenshot

idle.png


See that last checkbox?

Now we need this support on the iPhone too, and we're golden.

Gmail's IMAP supports IDLE too, BTW. And this worked great with Chattermail on my Treo, giving me push email. I don't have this on my 3G iPhone, which is a step backwards.
 
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