Hmmm. I have now idea what Opera was doing during that half an hour, because it didn't actually download and message bodies. I can tell this because every message body that I now click on gets downloaded individually.

More importantly, it appears to just as hopeless at threading as all the other clients I have tried. At least it allows you to select which folders are threaded, which not all clients do.

I don't think this will be replacing my use of SquirrelMail any time soon