That would be this bug.

Where can I get a copy of V 142

You did not mention where the empty folders are located. Q: Are the empty folders in a Pop or Imap account or in 'Local Folders' account ?

The bug mentioned is only about the 'Local Folders' account where folders are not displaying.

If you can see the folders then see if the following helps:

1. Check there are no filters operating on folder.

Via 'Menu Bar' toolbar: 'View' > 'Threads' > 'All' should be the only one selected.

Check Quick Filter: Select an empty folder Do you see any of the Quick Filter icons showing a blue indication meaning it's selected ? If yes, click on them to switch them off. examples: If 'Pin' icon is selected - it can be applying a previously selected filter. If 'Show only unread messages' icon is selected then it will display nothing if there are no unread messages.

2. Check to see if the index needs rebuilding.

• Right click on the Empty folder and select 'Properties'
• click on 'Repair Folder'
• Click on 'OK'

Are you talking about an imap account folder ? If yes, Logon to webmail acount via a browser and find out if those emails are still visible in same folder on the server.

If this is a gmail account - in webmail account: Are those subfolder labels selected to 'Show in Imap' ? If no: Please select the 'Show in Imap' checkbox.

if yes that 'Show in imap' checkbox is selected: If you cannot see the emails in the expected subfolder, then it's possible the label was removed but the emails are still in the 'All Mail' folder.

• select the 'All Mail' folder
• Look for emails that have no label applied - if the email is one you are missing then reapply the label of the subfolder.

Emails will then display in the subfolder, so when Thunderbird synchronises with server, it should see all of those emails.

If something deleted emails from the subfolder, then it's possible they by-passed the gmail Trash' which means gmail would only have removed the label and not deleted the email.

That makes me think what can delete emails ? I believe you may have experienced empty folders before back in february. Did that empty folders issue occur on the same subfolders? Have you got a setting which deletes emails after they are x days too old ?

If IMAP account : What have you got set up in 'Account Settings' > 'Synchronisation & Storage' Under 'Disk Space'

• select 'Synchronise all messages locally regardless of age'
• select 'Don't delete any messages'

If POP: What have you got set up in 'Account Settings' > 'Disk Space'

• select 'Don't delete any messages'

Also check the empty folders:

• Right click on empty subfolder and select 'Properties'
• Select 'Retention Policy' tab
• Select 'Use my account settings' OR uncheck that open and select 'Don't delete any messages'
• click on 'OK'

What Anti-Virus product are you using? Do you allow the Anti-Virus to scan your Thunderbird profile folders and files? I would advise you access the Anti-Virus and make an exemption to not allow scanning of the 'Thunderbird' folder in following location:

• C://Users/username/Appdata/Roaming/Thunderbird folder

OR at the very least you must not allow the Anti-Virus to 'fix' anything. Set it just to tell you about it but no auto fixing. Anti-Virus have no concept that a single mbox file may contain more than one email, so it can fix the entire file leading to loss of good mail. You do not want any Anti-Virus fixing anything.

Confirm what Anti-Virus you use and whether it was allowed to scan and fix, but now you have made profile exempt or at a minimum switched off auto fix option.

Here is my current thinking. I restored all my data from a months ago. Everything that was lost is there. I did a total file search and the folder data are there. See attached.

Conclusion. There is something wrong with the programme. How do I reinstall a previous version?

Further news. After reinstalling my current data some of the missing info has returned.

I should also have mentioned that I did run the previous suggestions but they did no change things

re : After reinstalling my current data

Please clarify as this could be important. Do you mean uninstall Thunderbird program and get a fresh download and reinstall of same version of Thunderbird ?

I do a full backup of my disc every night. I took a copy of my profile from the backup from a month ago and ran Tbird offline. When I did this most (possibly all) of the missing data was there. I did not reinstall the whole programme. Also a screenshot of my file structure shows that there is data in the folders I can't access. After reinstating my current profile the data was missing. At all times the folder names were there