This is the last Gmail for mobile Java release, which is no longer available from Google.
* Compared with Mail for Google 1.5 it adds:
~Support for multiple Gmail and/or Google Apps accounts.
~ Offline capability. You can use Gmail to read emails that you previously downloaded even when you have no signal. You canalso compose new emails with no coverage. When you hit "Send", instead of complaining about the lack of connectivity, Gmail will hold the newly composed email and send it when you move back into a area with coverage.
~Polling, Gmail will check for new email periodically, approximately every 5 minutes when it's in the foreground and every 20 minutes when running in the background.
~ Alerts, when new mail arrives Gmail will alert you. However it only vibrates once when a new email arrives, which is easy to miss.