I've been using Opera Mail since when the e-mail plugin has been detached from the old Opera browser.
I strongly believe that Opera Mail is the best e-mail client available, really.
I have tried, for instance, to use Thunderbird 31, but it needs a separate plugin to get a "threaded view", another one to get it minimized to the system tray. The combined view was hidden in a menu which was hard to reach.

But I feel like it's a pity when I see that Opera Mail has never been updated since its launch. It seems to be abandoned, while it deserves more attention.

My suggestion is to include an option which allows Opera Mail to be automatically started with Windows (I had to include manually a link in the startup folder), and to be automatically hidden in the system tray (I have to do it manually every time it starts).

I really hope Opera Mail will not be neglected. For me, its potential now is underestimated.