After struggling for hours yesterday to get Yahoo Mail to push, and failing.. I gave up. I called Apple, Apple had no answers. The way Yahoo's Push Mail works is it's Push-IMAP aka P-IMAP and uses the IDLE protocol that most IMAP servers have... So I setup my own server, I enabled IDLE with a 10 second check period. I setup my accounts in OS X's Mail and by default Mail uses IDLE if it detects it. It worked fine, I got new Mail within 10 seconds. I proceeded to sync the accounts with my iPhone and check the Mail on the iPhone. As soon as I read an email on my iPhone within 10 seconds it appeared as Read in OS X's mail, like it's supposed to. The problem is, unless I have the iPhone's Mail application open, it seems to ignore the IDLE protocol. It won't update any requests except for every 15 minutes when it pushes. Whether this is a bug or not, I have no idea. Apple needs to address this and soon.