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 open a hierarchy of Thunderbird email folders from 2 decades ago. 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. I thought that I could simple navigate within the Supernova GUI to open the MSF file, but all it does is show the text of the MSF file in a separaste tab from my email. No hierarchy of folders appears in the email folder pane. I realize that I can explore 3rd party tools, but these old files are native Thunderbird files. Surely there is a way to open them?