[TurboFool]

I've got to second the principle that more often than that will destroy battery life. I have four accounts, three of which check every 15 minutes, and I get dreadful life. Every five minutes would be unbearable. As well, every 30 seconds means it would roughly never stop checking, and your internet connection would go 24/7. It generally takes around 30 seconds or so to complete a mail sync, regardless of whether there's new mail.

Sounds like a push solution would suit you much, much better than constantly checking. You'd get messages only when there's actually mail, which would save you battery life and internet connectivity and keep your phone running more smoothly.

Without being rude, what is it that you're dealing with that you need 30-second intervals of automatically checking mail? I have my home email apps set to 1 minute and push for work, and I can't think of any circumstances where I'm expecting something that fast and can't simply hit the send/receive button to check myself.