If you're using IMAP instead of POP and your IMAP server supports IMAP keywords:

Create a label named test_label.

Right-click on "test_label" and goto "properties".

On the "IMAP" tab, set the keyword to test_label.

Add some (at least one) messages to that label.

Then, start Opera on the other computer and you'll see that the test_label is automatically created and that the messages you added to it on the other computer show up in the label.

Note though that rules and settings for the label do not get synced. Only what messages are in the label do.

If you're using POP, there's no support for syncing labels.