Help needed with backing up Outlook email folders and settings

MicroSoft programs are known to not recognise their own formats (although this is more documented with Word than with Outlook).

For this and for security reasons too, I would presonally recommend that you import your settings from Thunderbird, store the resulting files and use them after the upgrade.

Another option is the clearing up one: choose what emails you really can not leave with, send them to yourself and do not download them until you have done the upgrade.

Hope this helps although of course you do not need to believe this ...

ana