I think you're asking in the wrong place. You need to ask in a Norton support site about how they store backups. But whatever they do, Thunderbird won't be able to work directly with the Norton backup file. The intended use is that you backup, do the repair job and then restore the backed up data to where it came from, or create a new copy of the original data. If you do this and it puts the data back where Thunderbird looks for it, then yes, Thunderbird will be happy. If you were backing up for archive purposes, then I suspect Norton is not the best tool for the job; you need the backed up data to be accessible. For independent archival outside Thunderbird, I think I'd look for a way to save all the messages in eml format. The ImportExportTools add-on might be useful to you. But given an impending hard disk crash or similar, do the backup using Norton, replace or repair the computer and then restore your backed up data. So long as Norton has been told to preserve your Thunderbird profile, you should be good to go. You need it to include everything under AppData. It may not do this by default. The files you need will be hidden so may not appear in a regular file manager until you set it to reveal hidden files. For peace of mind, in your position, I'd make my own copy of AppData and all its children.