Opera Mail still exists as a standalone program separate from the browser, but it isn't being developed any more.
Opera 12.18 still exists as the latest (and last?) version of the old browser, and still includes e-mail.
The Windows versions of both programs were given a security update very recently, but that was a surprise, as most had assumed long ago that they were now abandoned.
I still use 12.18, although not the e-mail, and it's fine most of the time, but an increasing number of sites don't work properly using it now, and that will only get worse, and will not be fixed by Opera.