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

The simplest way for a 100% transfer is to copy the entire profile. Here are steps for that: : 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 you have already setup thunderbird and accounts, you can still get the Local Folders. If you're comfortable working with windows file explorer do this: - on old hard drive, locate the old profile at the users\<yourid>\appdata\roaming\thunderbird\profiles folder. the profiles.ini file at appdata\roaming\thunderbird will point to the proper profile - open that profile and click to the Mail\Local Folders folder and copy everything there - then, on new computer, paste it all in the Mail\Local Folders folder of the active profile - Do this when thundebird NOT running.