There is already an option in the KMail configuration (Appearance: System tray) regarding whether to show the KMail icon, and whether to show it only when unread messages. The icon also shows the count of unread messages. Can you add an option to choose whether the count represents unread messages in all folders, or unread folders in only the favourite folders? Reproducible: Didn't try
There is already the option "Act on new/unread mail in this folder" in the Folder properties, so this effectively is already possible, and will become more comfortable by extending inheritance (see Bug #310247). While the proposed approach is a perfectly valid alternative, it isn't compatible with the existing approach. Mixing the two concepts would lead to a overly complex UI and an obscure behavior. Additionally the proposed approach conflicts with Bug #169783. Therefore this unfortunately is a WONTFIX. At the same time, displaying more detailed information on the tooltip of the system tray icon is certainly possible. Please file a ticket if not yet existing.
won't fix, as per Bernd's testing
OK thanks, works for me! The label for that option "Act on new/unread..." is a bit unfortunate, because I do want KMail to download the new/unread mail (i.e. act on it, as far as I understand the term), so I never noticed this before. But the tooltip text is informative.