I installed Supernova after almost 2 decades away from Thunderbird. I created an Supernova IMAP account connected with my Gmail account. It was orders of magnitude easier than using Outlook. I need to copy a folder hierarchy of Thunderbird emails form 2 decades ago into my Gmail account. They take the form of associated *.msf files and, for each, either an extensionless MBOX file or a *.sbd subfolder with the same filename stem as the *.msf file. Copying these into Supernova's Windows folder for its "Local Folders email folder did the trick. I can see the old folder hierarchy and the messages therein. See Note [1] below. I tried to Ctrl+Drag the folder tree into the Gmail account, which causes some of the folder tree to be created, but none of the messages. I tried copying the swath of messages for each folder at a time, but nothing happens. I even tried copying an individual message, but no luck I assumed that this is because the Gmail tagging system is not compatible with idea of *nested* folders. So instead, I created *one* folder with the same name as *one* of the old Thunderbird message folders. I then tried Ctrl+Drag'ing the swath of messages in that old Thunderbird folder into the corresponding Gmail folder -- nothing happened. I even tried dragging *one* message from the old Thunderbird folder into the Gmail folder. Again, nothing happened. How can I copy folders in Supernova's "Local Folders" into my Gmail account? Alternatively, if I set up a corresponding folder in the Gmail account, only 1 level deep to be compatible with its tagging system, how can I copy swaths of messages from a Supernova "Local Folders" folder into the Gmail folder? Failing that, is it possible to copy one message at a time? '''Notes''' '''[1]''' This is posted at https://support.mozilla.org/en-US/questions/1440091. Unfortunately, I can follow-up with the answer. I get the message " An Error Occurred: Oh, no! It looks like an unexpected error occurred. We've already notified the site administrators. Please try again now, or in a few minutes."