PART-1: (downgrade) '''TB''' = THUNDERBIRD user:WayneMery pointed out [https://support.mozilla.org/en-US/questions/1314582 your original TB problem]. i see that, your TB upgraded & then after that you've lost access to your old emails & new emails, before the upgrade process happened, and after upgrade you've tried to add account but it warned you: ...server already exists. it appears that you've used Windows10 & Firefox to submit the problem, so i'm assuming TB was/is used in Win10. '''AV''' = Anti-Virus. Before you begin OPTION-1 in below, do this please: disable '''AV'''/FW/SS software's mail-protection, see last AV paragraphs [https://support.mozilla.org/en-US/questions/1315734#answer-1373022 here]. Restart TB, & see if that helped to solve. if not, then proceed to OPTION-1. DOWNGRADE '''OPTION-1''': in '''Windows''', your OLD EMAILS and your OLD TB PROFILE-DATA are inside this folder: “'''%APPDATA%\Thunderbird'''“ or “'''%APPDATA%\Mozilla\Thunderbird'''“ in Command-Prompt, if you try this command: '''echo "%APPDATA%"''' then it will show you the exact FOLDER LOCATION, what this '''%APPDATA%''' (env-var) means. You need to know/remember/write that exact location. for-example: "'''C:\Users\<WindowsUserName>\AppData\Roaming\'''" "'''%LOCALAPPDATA%'''" is "'''C:\Users\<WindowsUserName>\AppData\Local\'''" RUN WINDOWS-EXPLORER (FILE-BROWSER) AS PRIVILEGED USER: in Windows search box type '''explorer''', item will appear, Right-click on Windows-Explorer item/icon, choose/select > '''Run As Administrator''', or choose/select Other/More-options > Run As Administrator. Please goto new-TB > '''Help''' > '''Troubleshooting Information''' > press '''Ctrl+F''' to find word this & type: '''about:profiles''', click-on '''about:profiles''' > write down the active '''Root''' ("%APPDATA%") & '''Local''' ("%LOCALAPPDATA%") PROFILE folder/directory name(s) , they will have the word '''.default''' at-end (or other profile name at-end), and these folder/directory names begin with random alpha-numeric characters/letters/numbers, etc, like: "'''xxxxxxxx''.''default'''". for-example: "'''C:\Users\<WindowsUserName>\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx''.''default\'''" lets call this random alpha-numeric chars just "'''new'''.'''default'''". MAKE A BACKUP COPY OF ALL DATA INTO A BACKUP-FOLDER, BEFORE YOU DO TB DOWNGRADE: if new-TB or any TB is running, close+exit from it/all. Browse into the “'''%APPDATA%\Thunderbird\'''“ (or “'''%APPDATA%\Mozilla\Thunderbird\'''“) sub-folder location inside your Windows-Explorer. open the “'''Profiles'''” sub-folder. you may see multiple SUB-FOLDERS that ends with “'''.default'''” as last-word, and begins with bunch of random ALPHA-NUMERIC CHARACTERS, press '''Ctrl+A''' (to select all items inside the “Profiles” sub-folder), then press '''Ctrl+C''' (to create a COPY instruction in buffer memory), then goto windows "Desktop", create a sub-folder called "'''BAK'''", go inside that "BAK" folder on "Desktop", press '''Ctrl+V''' (to PASTE all files & sub-folder items inside the "BAK" folder, which were chosen by Ctrl+C). DO NOT DO ANY TYPE OF EMPTY RECYCLE BIN, DURING THESE TIME, UNTIL ALL IS BACK TO NORMAL. DO NOT DELETE ANY FOLDER/FILE, EITHER MOVE THEM, OR COPY THEM FIRST BEFORE DELETING. DURING DOING THESE DO NOT RESTART THE COMPUTER. TB = THUNDERBIRD DOWNLOAD TB SETUP/INSTALLER FILE/PROGRAM: download exact same v68 version that you were using earlier, or last of v68 series, from below location: https://archive.mozilla.org/pub/thunderbird/releases/ find '''version number''' & click on it > click-on "'''win64'''" > if you were using "en-US" locality edition, then click-on "'''en-US'''" > download the setup '''exe''' file. Make a folder "'''BAK-v78-x'''" in your windows DESKTOP: exit from all TB, if any TB is running. go inside the "'''C:\Program Files\'''" folder if you use TB 64bit , in your Windows-Explorer . goto "'''C:\Program Files (x86)\'''" folder if you use TB 32bit. find & click-once on "'''Mozilla Thunderbird'''" sub-folder , press '''Ctrl+X''' (to create '''Cut''' command for the selected item), go inside the "'''BAK-v78-x'''" folder in your DESKTOP, & press '''Ctrl+V''' (to '''move'''(cut+paste) new TB into that backup folder). RUN OLD-VERSION TB '''setup exe''' INSTALLER: make sure to do this during installation : do '''not''' select the '''option''' that says: Run it after installation <- '''unselect''' this option. finish setup. After installing older-version TB , YOU MUST [https://stackoverflow.com/questions/64980412/ STOP AUTO-UPDATE IN (OLDER-VERSION) TB] , ''(please upvote my Q+A there, if its helpful)''. in WINDOWS-EXPLORER, (make sure explorer is pre-configured to show full file extension), browse into “'''%APPDATA%\Thunderbird\Profiles\'''“ (or “'''%APPDATA%\Mozilla\Thunderbird\Profiles\'''“) sub-folder location, it has more sub-folders under it, these sub-folders' name will begin with random alpha-numeric characters & their name may end with '''.default''' or '''.default-bak''' or other ('''profile name''') word, if you see a sub-folder that has "'''new'''.'''default'''" (goto top side to find out what this "new''.''default" means), then that is your last upgraded (new) TB version's default profile. go inside each "'''xxxxxxxx''.''default'''" profile sub-folders, try to find a file named "'''abook''.''mab''.''bak'''" or "'''history''.''mab''.''bak'''", etc, you have to (select those '''.bak''' files, and) '''copy''' (Ctrl+C) those files inside EACH "'''xxxxxxxx''.''default'''" folder that is now used by the last installed old-version TB, as it's default profile, (just copy, if asked/promted to overwrite, don't do overwrite, do 'rename' or 'skip'), and then rename "abook''.''mab''.''bak" into "'''abook''.''mab'''", and rename "history''.''mab''.''bak" into "'''history''.''mab'''", etc, "abook''.''mab" is your address-book file, "history''.''mab" is history records file, etc. You MAY also have to fix some settings in "'''pref''.''js'''" file , it is inside profile folder , make a copy of this file, & right-click on it & open it with a text-editor / notepad++ app, etc. GOTO "'''Command-Prompt'''" or '''Run''' WINDOW: run this command to '''downgrade''' if you use TB (64bit) , include the double-quote symbols in command: '''<code>"C:\Program Files\Mozilla Thunderbird\thunderbird.exe" --allow-downgrade</code>''' if you use TB 32bit then use below command: '''<code>"C:\Program Files (x86)\Mozilla Thunderbird\thunderbird.exe" --allow-downgrade</code>''' When TB (Thunderbird) appears on screen, first thing you do is [https://stackoverflow.com/a/64980413/3553808 Disable Auto-Update in Thunderbird] ''(please upvote my Q+A there, if its helpful)'': goto these below sub-folder locations, and delete "'''updater''.''exe'''" file, if it exists there: “'''C:\Program Files\Mozilla Thunderbird\'''“ “'''C:\Program Files\Mozilla Thunderbird\updates\'''“ “'''%APPDATA%\Thunderbird\updates\'''“ “'''%APPDATA%\Mozilla\Thunderbird\updates\'''“ if you use 32bit TB, then also check these folders: “'''C:\Program Files (x86)\Mozilla Thunderbird\'''“ “'''C:\Program Files (x86)\Mozilla Thunderbird\updates\'''“ Please goto old-version TB > '''Help''' > '''Troubleshooting Information''' > press '''Ctrl+F''' then type this to find this word: '''about:profiles''', click-on '''about:profiles''' > write down the active '''Root''' ("%APPDATA%") & '''Local''' ("%LOCALAPPDATA%") folder/directory name , it will have the word '''.default''' at-end, and folder/directory name begins with random alpha-numeric characters/letters/numbers, etc. lets call this random alpha-numeric chars just "'''old-version'''.'''default'''". write it down. check if older accounts & older emails, older folders, etc are back in v68 series TB, or not. if old data & settings are not yet back, then exit/close TB. in Windows-Explorer, goto older-version TB's profile folder location: “'''%APPDATA%\Thunderbird\Profiles\old-version''.''default'''“ you have to check & make sure that correct '''.mab''', etc files exist in this "old-version''.''default" folder, So IF those '''.mab''' ("abook.mab", "history.mab", etc), etc files do not exist here, then copy-paste those from other "xxxxxxxx''.''default" profile location(s) into this "older-version''.''default" profile location, that is used by older-version v68 series TB . Also fix the "'''pref.js'''" file, shown 2-paragraphs above ). exit/close TB, restart TB, this time it should reload all older data back. if old data is still not back yet, check PART-2 TB = Thunderbird . FF = Firefox. More info: [http://kb.mozillazine.org/Files_and_folders_in_the_profile_-_Thunderbird] (VERY HELPFUL) [https://www-archive.mozilla.org/support/thunderbird/edit TB Config Editors & Config Files] http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Thunderbird (for older TB, but VERY HELPFUL) https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data https://www-archive.mozilla.org/support/thunderbird/profile (for newer TB, profile folder location) http://kb.mozillazine.org/Profile_folder_-_Thunderbird (for older TB, but Very HELPFUL) http://kb.mozillazine.org/Go_back_to_an_old_version_of_Thunderbird (for very old TB, but may be helpful)

FWIW, Pam's original problem, where she still needs help, is at https://support.mozilla.org/en-US/questions/1314582

PART-02 if TB (in '''Windows''') still has not loaded older data+settings, etc yet: exit-out / close TB, if its running. run this command: '''"C:\Program Files\Mozilla Thunderbird\thunderbird.exe" -P --allow-downgrade''' if you use 32bit TB, then run below command: '''"C:\Program Files (x86)\Mozilla Thunderbird\thunderbird.exe" -P --allow-downgrade''' that '''-P''' is for profile-window, a small window will appear from TB, & ask+allow you to choose a profile, choose a profile that was used by older TB, (do not choose the "new''.''default" profile that was used by the new-version-TB ). restart TB , check again, if you have got back older data+settings, etc. it should show all old data+settings, as we are using old-profile. check other OPTIONS mentioned [https://support.mozilla.org/en-US/questions/1316147 here]. '''TB''' = Thunderbird. Check Other HELPFUL related ANSWERS, inside these pages: https://support.mozilla.org/en-US/questions/1316147 (various OPTIONS: downgrade, second-TB, file-transfer) https://support.mozilla.org/en-US/questions/1304550 (downgrade TB v78+ series into v68 series) https://support.mozilla.org/en-US/questions/1313244 (Get emails from older TB profile) https://support.mozilla.org/en-US/questions/1312300 (Undo v78, Get back v68) (do not do "Empty recycle bin", if you're instructed to do so there) also check [https://support.mozilla.org/en-US/questions/thunderbird TB-SUMO] (this site), & search for TB problem fixing, or downgrade or other solutions.