Push email support is one of the iPhone 3G’s most anticipated features, but unfortunately it won’t work with every email account. The latest iPhone software – iPhone 2.0 – can’t automatically turn any email account into push email. It can only instantly send new messages to your phone if your email service supports push email.

The new iPhone 2.0 software supports Microsoft Exchange services and Apple’s Mobile Me service (the replacement for Apple’s .Mac). Apple claims Mobile Me is “Exchange for the rest of us” and it can push email to devices running iPhone 2.0 as well as sync with Microsoft Outlook on a Window’s PC or the Mail, Address Book and iCal apps on a Mac.

The new iPhone’s main settings menu offers a new icon labelled Fetch New Data that lets you enable push email. You can also schedule the phone to automatically check non-push email services at 15, 30 or 60-minute intervals, otherwise only manually.

Which email providers work with push?

Push support depends on your email provider. The original iPhone supported push email with Yahoo! by routing email through a dedicated server but overall the service was unreliable. The same server is still used as the default Yahoo! email set up under iPhone 2.0 but if it doesn’t work you can modify the settings by going to Other and manually set up POP3 Yahoo! access. Gmail does not support push email, only IMAP or POP3.

What if I use Gmail or email from my ISP?

One work around is to forward your existing email address such as a Gmail account to your Mobile Me account. Another option is to create server-side filters on Gmail to only forward emails from certain senders to your Mobile Me address so you’re not flooded with spam.

You can also configure Mobile Me to automatically check your external POP3 email accounts, but this won’t get emails from Gmail to your phone as quickly as it would if your Gmail automatically forwarded them.

How Much Data does push use?

One thing to keep in mind is that push email uses more data. The iPhone 2.0 mail client only downloads email headers from IMAP and POP3 servers to save on bandwidth. When using push email services, the phone automatically downloads the body of the email and small attachments – meaning you should avoid push email unless you have a generous monthly data allowance.

The iPhone will also disable its Wi-Fi connection when sleeping or witching over to the mobile data network. This means your push email will come down over the mobile data network while the phone is at rest, even when you’re in a Wi-Fi network.