If anyone's still interested, I deleted every email account, rebooted and then re-added one. Same problem. Something in that install of Opera has cache'd messages that I've long since deleted from the mail servers.

Anyway, thanks again.

Would rather keep using my existing one tho.

For POP accounts at least, you can close down Opera and delete the uid file in the pop3 folder in the mail folder. They're numbered by account (see accounts.ini for what number each account is).

What that will do is cause Opera to reset its tracking of messages it has previously fetched (which should fix the problem). This will cause Opera to refetch all messages in the Inbox though. If any of those messages have already been fetched, you'll need to delete the old copies and keep the new ones as the old ones won't be tied to the copies on the server like the new ones will.

If that doesn't work, you can check the database. It sometimes fixes things.

If that doesn't work, you can try to see if some message in the "Inbox" is confusing Opera. For example, with webmail or IMAP, move all messages in the "Inbox" to another folder. Then, see if things work fine from then on. If they do, it's probably a certain message that was in the Inbox (and now in the other folder) that was causing the problem.

You can try logging the connection to see if the log shows anything. For example, it might show an error once it hits or certain message or fetching of messages might stop when Opera hits a certain message.

As for IMAP, in Opera, if you're having a problem with a certain IMAP folder besides "Inbox", you can goto "Menu -> Mail -> IMAP folders", unsubscribe from the folder and then resubscribe. If that doesn't help or the problem is in the "Inbox" folder, you can delete the IMAP account and add it back in to fix things. Make sure you don't have low-bandwidth mode set for IMAP accounts though.

If none of that works, you'll have to fix the mail folder.

Would rather keep using my existing one tho. I have mostly POP accounts and they're the ones that retrieve a zillion copies of the same email.

If it helps, it seems that my one IMAP account is also malfunctioning; repeatedly retrieving a test email i sent it but incorrectly labeling it "(No subject)".

I don't use labels.

I've had this configuration for over two years without incident and I haven't knowingly changed any settings recently. Where to from here?

Download the Opera installer

To be clear, I mean Opera 12.17 for example.

POP.

Version 12.17
Build 1863
Platform x64
System Windows

This new installed version doesn't appear to have a mail service ..

Any ideas?

Download the Opera installer, launch it, click "options", set "install path" to a folder on your desktop, set "install for" to "Standalone Installation (USB)" and install. In that Opera, set up your account fresh. If it's a POP account, make sure you don't uncheck "leave messages on server" (also, make sure the POP settings at mail.google.com are set to auto-remove messages when fetched)

If it works fine there, then it's just something messed up with Opera's mail folder probably. What to do about it depends on whether you're using IMAP or POP (and whether you're using Opera's labels or not).