Answered in https://support.mozilla.org/en-US/questions/1324463

your older emails should be inside older TB-profile.

a TB-profile is generally located here: • in windows: "%APPDATA%\Thunderbird\Profiles\<profile-name>\" that is usually: "C:\Users\<WindowsUserName>\AppData\Roaming\Thunderbird\Profiles\<profile-name>\" • in Linux/Unix: "~/.thunderbird/<profile-name>/" or "~/.mozilla-thunderbird-<profile-name>/" that is usually inside main/default volume: "/Users/<Linux-Unix-UserName>/.thunderbird/<profile-name>/" or "/Users/<Linux-Unix-UserName>/.mozilla-thunderbird-<profile-name>/" • in macOS: "~/.thunderbird/Profiles/<profile-name>/" that is usually inside default volume: "/Users/<macOS-UserName>/.thunderbird/Profiles/<profile-name>/"

TB = Thunderbird.

inside the current TB goto main menu > Help > Troubleshooting information > about:profiles > Root directory. find the line "Default profile: yes", in that section , in the "Root" directory line, the last sub-folder is your TB's TB-profile folder. if Open folder/location button exist , use that to open the location inside File browser. remember that last sub-folder's name , lets call it "TB-new-profile-name" folder.

go backward/upward one folder, in File browser, you will see similar looking more sub-folders. other sub-folders there which are not same as TB-new-profile-name , then one of those sub-folder is your "TB-old-profile-name" folder.

TB installation folder varies based on Linux/Unix distro.

if your TB in your Ubuntu variant/distro is installed here: "/usr/bin/local/thunderbird/" and, if your "TB-old-profile-name" folder is here: "~/.thunderbird/TB-old-profile-name/"

then use a Terminal window in Ubuntu, and start TB with a different TB-profile, in this way: "/usr/bin/local/thunderbird/thunderbird" -p "~/.thunderbird/TB-old-profile-name/"

if above old TB-profile folder is not correct old-TB-profile , then use above command again, but this time use another/different old TB-profile sub-folder name , which are inside the "~/.thunderbird/" sub-folder.

if above old TB-profile folder is correct old-TB-profile , then to use that old TB-profile permanently , use such command: "/usr/bin/local/thunderbird/thunderbird" -ProfileManager or try this: "/usr/bin/local/thunderbird/thunderbird" -P a profile choosing/selection window will appear: https://www-archive.mozilla.org/support/thunderbird/profile select the correct old TB-profile name , & select "Use this profile permanently" option or similar option. Only "profile-name" portion will be shown inside profile selection window , not the "xxxxxxxx" portion/part of the full profile-name of sub-folder: "xxxxxxxx.profile-name"

then double-click on TB icon , it will start the TB with the old profile . no need to use long command to start it.

@atErik,

Please take care to look at the KB articles - they already supply this information in detail - for example https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#thunderbird:linux:tb78. If they are not accurate, please take time to improve them. Thanks

Thanks all for the replies.

It turns out that thunderbird profiles are not stored in the standard .thunderbird folder on Ubuntu when using the newer snap.io packages that Ubuntu has started using lately.

Now the profiles are stored in a users home directory: ~/snap/thunderbird/common/.thunderbird... etc.

I learned of the new location from a user on a Ubuntu irc channel and confirmed by doing a fresh install of Ubuntu then going to Help/Troubleshooting Information/Profile Directory/Show Directory.

I tried restoring my profile from backups but my DejaDup/Duplicity restore function is failing so I'm off to the next problem.