https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

If the accounts are POP, the transition is simple. Just copy the entire profile with these steps: Here is the link for moving a profile in Windows when installed in default location: https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer here is the info in brief steps: # ensure thunderbird is NOT running on old machine # enter %appdata% in search window on task bar and press Enter key # this should open windows file explorer in Appdata\roaming folder # highlight the Thunderbird folder and copy to external media # ensure thunderbird is installed on second computer and NOT running # enter %appdata% in search window on task bar and press Enter key # you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This may prompt to overwrite an existing folder of same name. allow it # start thunderbird and all should be there If the account is IMAP and closed, you should first COPY (not move) all messages in the CLOSED acccount to Local Folders and then do the above steps.