If you allowed the Anti-Virus to 'fix' the problem, then it would have deleted the entire file containing emails because AV products do not understand the mbox file contains more than one email. It would not have deleted the indexing file and so you would now see headers to emails that do not exist. Hence no body.

To fix the index:

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

This will create a new index file for that folder which will show you the real contents of that folder. Fixing the index does not delete emails.

If the AV product has only quarrantined the file then try restoring it.

If this is a 'Pop' mail account and you have kept a copy of email in server Inbox: In Thunderbird

• 'Help' > 'TRoubleshooting information'
• click on 'Open folder' button

A new window opens showing the contents of you profile name folder.

• Exit Thunderbird now - this is important.

• click on 'Mail' folder
• click on pop mail account name folder.
• delete the 'popstate.dat' file

The popstate.dat' file keeps a record of what has been downloaded so preventing redownloading emails.

• Start Thunderbird

A new popstate.dat file is created and emails in server Inbox will begin to get downloaded.

If this is an imap mail account: Logon to webmail account via a browser and see if emails have been removed from server. If no emails on server, then you will need to use your last backup and an addon called 'ImportExportTools' to import mbox files back into 'Local Folders' mail account and then try to copy them back into the imap mail account folders to put them back on the server. ImportExportTools addon: https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools/

For future reference, I use this method to locate identity of a bad email so that AV does not mess with the files in Thunderbird profile folders.

If AV says there is a bad email, do not allow AV to fix it.

• Create folder on desktop called 'TB-Emails'
• Highlight emails in a folder (Ctrl+A will hightlight all)
• Right click on highlighted emails and use 'Save as'.
• Save emails as .eml files in the 'TB-Emails' folder.

Each email will now be saved as a separate file.

• Use AV to scan 'TB-Emails' folder. It will locate which email(s) are bad and only fix those bad emails.
• Then you can locate that email in Thunderbird and delete it.
• Empty the 'Trash' folder
• Right click on folder and select 'Compact' to fully remove the deleted but hidden email.
• Then delete the contents of the 'TB-Emails' folder and empty the 'Recycle Bin'

That's great thank you, though it scanned 2550 items in 1second flat, is that sound right?