Whoa!
What do you mean, Opera no longer has a mail client? I've been using it for years. Then, today, my update does not seem to have it. I never saw any notification. When did this happen? I switched to Opera because I couldn't get Thunderbird to work properly. Now Opera is gone? YYYIIIKKKEEESSS!!!
Try and do a little leg-work (i.e. searching) BEFORE you panic. Opera has a Standalone mail client and it works. It's essentially the mail client that was part of the older Presto (i.e. 12.17 and earlier) suite with the browser and other features hidden. Rumor has it that Opera will not continue the development of the mail component since the older suite is no longer being developed. That does not mean that the mail client will no longer work, however, one might consider exploring other mail options (i.e. The Bat, Thunderbird, Outlook, etc.). You never received any notification since Opera 12 is not being updated and the new version of Opera is not an update but an entirely new browser, rewritten from the ground up.