How to move Thunderbird with local folders to new computer

You don't describe what you've done so far, and I don't understand what you mean by 'local folders being assigned a different ID.' I wonder if you have been making this more complicated than necessary. If you copy your entire Profile from the old installation to the new one, all your accounts, messages, folders, and preferences will transfer. Things will pickup pretty much pick up where they left off. There should be no need to "change the target address". Here are some articles about the Profile and how to move it. Move Thunderbird data to a new computer https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer Profiles - Where Thunderbird stores your messages and other user data backing up, restoring, moving https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data And here is a good method to copy a profile to a new computer, courtesy of forum user david: 1) ensure thunderbird is NOT running on old machine 2) enter %appdata% in search window on task bar and press Enter key 3) this should open windows file explorer in Appdata\roaming folder 4) highlight the Thunderbird folder and copy to external media 5) ensure thunderbird is installed on second computer, started once and NOT running 6) enter %appdata% in search window on task bar and press Enter key 7) you should be in Appdata\roaming folder. DELETE the thunderbird folder there 8) now paste your copied thunderbird folder there. 9) start thunderbird and all should be there