I'm gradually moving from BlueMail to Thunderbird. BM lets me create new folders (I use "hold" and "action") to which I move things I've read and want to keep until downloaded to Thunderbird on my PC. Other stuff goes to trash and (along with spam) gets deleted. This program's documentation SAYS you can create "new subfolders" but I can't find out how. "Manage folders" doesn't seem to help.