Re: Aqua has a "Push mail session duration" parameter. What is it and what are the tradeoffs in its allowed settings (30 minutes, 1 hour, 2 hours)?
IMAP guarantees that an established and logged in connection will not be disconnected by the mail server for at least 30 minutes.
I'd say leave it at that, or try 1 hour. This won't have a big effect on battery usage - since even "every 25 minutes" (which is what the "30 minutes" setting actually does) is not _that_ often, compared to everything else that push mail has to do.