It seems claws scans all folders or so. It takes a few seconds. Most of the time mail will be sent only to INBOX, and then filtered to be moved to sub-folders. I want the new mails to show up in the sub-folders, but I don't think scanning them is strictly required. No, I don't want to configure this manually, because that means I might do it wrong, and miss mail that is added to various sub-folders for obscure reasons.
Shouldn't this be sent to the user's mailing list instead?