According to this article, Get to know OS X Mavericks: Apple Mail 7.0 from Macworld it does the following:
In the General screen of Mails Preferences window, youll find a new option in the Check for new messages pop-up menu called Automatically. This option essentially allows Mail to support push-style message retrievalyou receive new messages immediately, rather than at the next scheduled check.
Thanks... and interesting. I checked that setting on my machine and that setting was still on Manual like it always has been for my iCloud account (I did a Mavs upgrade from ML), and I still get push email. I wonder if that setting is for generic IMAP accounts and iCloud knows to make it push on its own.
Seems to make sense that that setting would apply to accounts that don't normally use push. Since I don't have an iCloud account and haven't upgraded to Mavericks yet I can't confirm that theory though.
Yes Apple's iCloud have the new IMAP push in servers that host IMAP. Both iCloud and GMail do Push iMAP and work good on my 10.7.5 Mac Book Pro and 2008 MacPro on 10.9.0.
Now I know most ISPs don't like doing email like they really don't like DNS. That is why so many people have gone to Google or iCloud. Plus the crush of soliciting email (SPAM) is crushing email for most everybody. A great email SPAM filter is must these days. So get a public email address for buying things online, etc. Then have a personal email address that you only share with family, close friends, relatives. This way you can always protect yourself.
That IMAP Push uses the IMAP "idle" command for push. If you look in Mail app (even with iCloud) settings there is a toggle for the idle command. If the IMAP server supports idle that is what gives you push.
What Dew and I were trying to riddle through was exactly what this new "Automatic" setting really does. If I have the IDLE box checked I get iCloud (IMAP) mail pushed with the setting on either manual or automatic, so the settings does not seem to do anything.
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If that's the case with IMAP then I'm thinking it's for POP email, to get the mail as it's available rather than waiting for a predetermined amount of time to check.
I don't think POP is capable of that. The Mail client would have no way of knowing a new message was present on the POP server.