It appears that I actually got the old integrated mail client working again!

The solution makes absolutely no sense, but I'll write it out in case someone happens to run into the same problem. I was just fiddling around with all the settings I could think of, and this is what worked for me. When you press the monkey wrench icon that appears next to your email address when you have selected one of your accounts, you can select "IMAP Folders". I unselected the inbox folder from there and then reselected it, after which everything was magically alright once again. With repeat and rinse for all the other accounts I have, naturally. Go figure, but I'm glad I can continue using my favourite mail client.

Thank you for all your help! Have a great summer!

Ok, thanks for the info!
Trying to locate that will be my plan B if I can't get the integrated one working.

Also, am I correct in that the new Opera Mail client (the non-integrated one) is only available for Windows and Mac, not Linux?

Oh, I see. The integrated mail client is actually one of the main reasons why I have been using Opera for ages...more than ten years I think. So I'd be happy if I could continue using it. Plus I have been using the label system rather heavily, so migrating to some other mail client would be a hassle.

Ctrl+k doesn't do anything, and neither does clicking the "send+receive" button. "Check for new messages every #minute" is checked and has a number. As far as I can see there doesn't seem to be anything wrong with the settings, but I might of course be missing something.

Thank you for helping me out!

First of all, sorry if this has already been asked. I might have been bad at searching, but could not find an answer to this in the forums.

The thing is, my Opera mail stopped receiving new mails a few of days back. It took me a couple of days to notice this because there are no error notifications (dumb I know), and now I can't remember if there was a software update for Opera or not. I'm running Ubuntu.

I can send mail just fine and my mail settings are unchanged. I get no error notifications. The new mails just... don't appear. I'm rather perplexed, so if you have any suggestions where to start looking for a solution, I would be grateful.

Edit: This is true to both my gmail and my university account, so I think this must be a problem with Opera.