Just got my first iMac. No options for push in email accounts. I'm using Exchange and Yahoo. Polling every minute. Why can you get push on iPhone and iPad and not on iMac???
You can get push email on your Mac using the default Mail app with an IMAP email service, like Apple's free iCloud for example.
I think Yahoo does support IMAP's IDLE command, but I believe you need a paid Yahoo Plus email account for this. Here is some info on Yahoo Mail and IMAP that might help you.