I wish "backing up" was really feasible for me, I really do. But can you imagine how expensive it would be to do that for 4TB of data?

Yes, there is. Do backups of the mail folder and, when a more serious issue happens, just use the backup to recover most of your data or even your entire data depending on how often the backups are done.

This is also not a fix for my current problem.

But why this is happening? You need to try to find the cause of the issue or it will continue to happen.

It's only ever happened following a crash, which there is no "explanation" for. But it's literally brought my ability to use the internet to a standstill every time it's happened. And it shouldn't be happening to begin with.

But then again, the fact that Opera has stopped development was a devastating blow to my productivity to begin with, one that I still haven't really fully recovered from. Thankfully I just discovered Vivaldi, and as soon as that gets on stable footing, I'll be making that switch, hopefully for life.

Already covered above, but the old post for how to do these things is archived here.

This is flagged as a harmful website by my antivirus.

And the only thing I've seen people say to do to "fix" this problem isn't really a "fix", it's a really messy band-aid (more like gauze-mummification) for a problem that has completely destroyed productivity on more than one occasion. There is no feasible reason why this can't just be outright fixed when all the messages are clearly still there but just not loading. It's just really sad that no one has even bothered to figure out what is causing this to happen and would instead rather force people to do manual maintenance on their (probably extremely huge) databases in order to step around the issue like a pile of broken glass.

Is there still no better way to fix this problem that shouldn't exist in the first place? This is like the third time it's happened to me, I have over a hundred thousand messages across 100+ RSS feeds and several email addresses, and this is simply not a viable thing to do. How has no one automated this yet? I never thought I'd say this, but the moment I get this fixed, I'm switching to Thunderbird.

Actually the only thing I'm worried about at all is my RSS feeds, all of my emails are accessed through IMAP so I don't even care about "losing" them locally, but the saved RSS feeds simply cannot be recovered if I can't fix this.

I've already tried "solutions" (e.g., automated scripts) floating around that purport to convert Opera's notes.adr to Evernote and Zotero, neither of which worked (Evernote couldn't import the file for whatever reason, and the python script I found for Zotero just broke at some point, probably because my Opera notes are riddled with Unicode text in multiple obscure languages). I need to find SOMETHING that works, anything at all at this point would work well enough, I just need get them out of Opera without having to do it all manually because I have literally hundreds of notes. At this point I think even exporting them as .txt files would suffice.

If you're talking about the files in AppData\Local\Opera\Opera\mail\store\accountx folders, it looks like they are, but they're all jumbled into random folders and I don't really know what I would do with them.

Still not been able to fix this problem. I'm hoping to transition my newsfeeds and stuff to Opera Mail, but I don't want to risk losing anything that might yet be salvageable.

That setting is set to 0 by default. I've already tried setting it to 1, restarting, then setting it back to 0 and restarting again, and nothing.

So after I suffered a system lockup where I had to hard-reset my computer, I launched Opera to find all of my newsfeeds and email folders rather spookily blank. They are NOT empty - I can still see many, many entries in my newsfeeds, except that they are completely and utterly blank - no name, date or source, and when I click them it maintains "no message selected". Emails fixed themselves automatically due to the magic of IMAP, but my newsfeeds have thusfar eluded me. Any new updates that are captured by my feeds display properly, in their correct folder, but on top of countless blank entries where my old feed data was. Is this fixable, or is it a permanent corruption?

For clarification, this is roughly what it looks like:

http://i.imgur.com/IhT3eek.png