Opera's mail client that is part of the current Opera 12.5x release has been split off as its own app in preparation for the Chrome/Blink/Webkit-based Opera 15 release. It has now hit 1.0 and should be quite stable, so I've packaged it up for release. I wanted to do a quick one day dev test just to ensure everything is sorted.
This app has been officially released
Please report back.