I am not a Wndows 10 expert. I just use it because that's what is provided by my employer. But I am surprised that the installer doesn't offer a way to automatically preserve and re-use all your personal data. I'd have thought you'd have more than just your email to look after. Anyhow, if you're concerned just about your email, you need to make a backup of Thunderbird's profile. This contains your messages, filters, settings, address books, extensions and so on. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data