So what do you do if your target folder is a subfolder and the parent won't open? Just drop it on the parent folder without knowing where it will land?

No. Obviously I have the target folder or subfolder in sight when I drag another folder into it. However, your question does raise an important scenario: If I wanted to drag a folder into a folder that is buried deep in a list of subfolders of a parent folder that is closed, then the ideal behavior would be that if I hover over the closed folder (not less than 2 seconds) it should then open, and so on down the line. But if you simply drag & drop a folder into a closed one then that's where it should go, and stay closed. But having it open instantly without the 2-second hover period is catastrophic. Here's why this is so important for me: I have a top level folder called ORDERS. Under it I have: Orders A-C Orders D-F Orders H-J Orders K-M etc, etc. And under each of these is another group of folders by customer names (some 70 to 80 under each letter group).This tree exists because without it I would have to scroll endlessly to arrive at the desired target subfolder to drop a particular message (or order folder) into. And it is a Huge pain when the long subfolder tree instantly opens upon drag release, forcing me to endlessly scroll again, or jump to the top to close the trees again to drag the next folder to its destination. This never used to happen in the past. Of course I also use Axel Grude's QuickFolders app, which is a godsend.