I am trying to replace Thunderbird which manages 7 IMAP accounts with ~30 folders. My research indicated Claws might be worth a try, so I am doing just that, however there is one thing I can't seem to find out:

It does not automatically show new messages in folders, while Thunderbird did just when they arrived. This is not the same as periodic check, because those are all IMAP accounts and I think in TB there is something like IMAP idle...

I am not sure how is it called, but what it does is messages end up in my TB folders as soon as they arrive, without the necessity of TB having to go through all Get New Mail ordeal.