For anyone interested in this issue/question, I have emailed the good folks at Boxcryptor and this is in fact the correct procedure for those using Thunderbird. And, as for any backups you may be doing of those same Thunderbird "Local Folders" to keep a copy same in case of any issues, you can backup either the original Dropbox "Local Folders" (they will be backed up unencrypted), or, point the backup program to the Boxcryptor location. In the case of the Dropbox location, they will be copied unencrypted (the copies are unencrypted as they are move out of Dropbox to the backup location), or you can point the backup program to the Boxcryptor location (as those are kept unencrypted on your local location).
