We would like a non-intrusive way to tell the user that new mails are available in a folder.

I'd like to:

• avoid actual notifications
• potentially avoid the unread count (unless we deem that useful)

I think a simple colored highlight of a folder with new mails, that gets cleared when selected, would already be good.
I also think we could keep this a runtime only thing (so we don't end up with lot's of folders that are highlighted).

Because there is no good IMAP solution in sight for actual notifications (because noone has NOTIFY support, and IDLE is single folder only),
a periodic check of all folders could be implemented. If we only stat the folders and check the message count that should be reasonably efficient,
and could then result in a new-mail notification.