re :Inbox clearly show the data to be gone e.g. resetting X-Mozilla-Status: to 001

If you accessed the profile folder and located the 'Inbox' mbox file. Opened the Inbox using eg: Notepad and could see emails, hence trying to reset X-Mozilla-Status, then the emails are there and you have not done the process correctly. BTW...001 is not correct...0001 is correct.

So please follow the following instructions and retry as you may have missed out on one of the processes or if you entered 001 instead of 0001.

In thunderbird

• Help > TRoublshooting Information
• click on 'show folder'

a new window opens showing profile folder name

• Close Thunderbird now - this is important

• click on 'Mail' for POP mail accounts
• click on mail account name

you should see the 'Inbox' mbox file - it has no extension.

• Open the 'Inbox' file using Notepad

Each email will start with these lines: this is an example

• From - Sun Dec 28 18:14:40 2014
• X-Mozilla-Status: 0001
• X-Mozilla-Status2: 00800000

Use 'Edit' > 'Find' Starting at the top use the look for this line: X-Mozilla-Status: 0001

Make sure each X-Mozilla-Status: has the number 0001

• edit the number as required working down through the document.
• Save the file.
• delete the 'Inbox.msf' file. A new one will be auto created.
• Restart Thunderbird.

that should get emails back in Thunderbird Inbox

If this is an Imap account: The emails will be in the 'ImapMail' folder.

If it fails to put back on server and seems to delete them again. Go through the same process again - making sure TB is closed/exited first. Do the correction again eg; X-Mozilla-Status: 0001 Then save file as eg: OldInbox then put the 'OldInbox' file in 'Local Folders' account which is under 'Mail' folder not 'ImapMail'. Restart Thunderbird.

This time you should see all those emails in a new folder called 'OldInbox' in the 'Local Folders' account. Test one email first: Use the right click on email 'copy to' and select the imap mail account Inbox. Allow some time for computer and server to synchronise and then check to see if the email is on the server Inbox via webmail. If yes, then copy more emails over. You can then use the 'OldInbox' as one of your backups, but you should backup the entire Profile. You can do that manually by copying the Profile folder name usually called xxxxxxxx.default. Where the x's are letters and numbers. Make sure TB is closed before copying that folder. Store it on external usb or disk drive.

Thanks for your responses:

The account is POP3 which I should have included.

The format I used in the reset X-Mozilla-Status was OK I only changed to 9's to a 1 and recovered that info - I just got the no of zero's wrong in my post.

The emails in the Inbox which I did reset the X-Mozilla-Status for successfully were only a few emails received and deleted after the data loss had occurred - no trace of the lost emails (50 or so) was present in any form in the Inbox data file i.e. no opportunity to reset status as the data was absent.

The only process used in Thunderbird was the Repair folder option when the problem surfaced and not the Compact option.

On enacting Repair the data disappeared both times and couldn't be recovered.

ok I understand that not all were recoverable. You have provided good feedback on your files and processes you have performed and I can offer an explanation of what is most likely to have occured.

When the emails originally appeared blank, they had already been lost, but the index file had not been effected and so still showed the headers, but it could not hook up to the actual email because it was not there - hence blank. When you repaired the folder, all it did was look at the list of emails still in Inbox and show what was there. Repairing the index file had no effect on the emails themselves and was the correct procedure in the circumstances.

X-Mozilla-Status: 0009 means those emails had been hidden because they were marked as deleted. Had you compacted the folder it would have detected those marked with 0009 and removed them completely thus freeing up needed space and reducing the file size. This reinforces the fact that if you detect any type of corruption you should not compact any folders until you have checked the files themselves. You had correctly not compacted folders before seeing what was going on in the file.

So this tells me compacting did not cause this because you located some of those emails marked with 0009 still in the mbox file. Also compacting would have synched the index file with the mbox file, but as you know this did not occur because you did this manually by repairing folder. Compacting will only cause a loss if the mbox file was already corrupted.

In this situation, where only the mbox file was effected, the most likely cause is an Anti-Virus product. AV's have no knowledge of the .msf file and it's purpose and so leave it alone. The AV tried to fix the mbox file and ended up messing it up completely and removing emails that most probably were all ok.

I would advise that you do not allow AV to scan Thunderbird folders on startup and also there is practically no gain in scanning incoming and outgoing mail. Thunderbird by default does not allow remote content and any attachments you open will be scanned anyway. Although you should never open anything that sounds suspicious.

If you prefer to keep scanning, then I would advise you create regular backups of your Profile name folder. It may also be a good idea to force the AV product to ask what to do when it detects anything, so giving you a chance to not quarantine it. AV products have difficulty in understanding that an mbox file can have loads of emails written to it one after the other, they just see it as one file.

Hope this helps to try to explain what is the most likely cause.

Useful links:

• http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Anti-virus_Software
• http://kb.mozillazine.org/Email_scanning_-_pros_and_cons
• http://kb.mozillazine.org/Privacy_basics_(Thunderbird)

Thanks very much for your help. Even though I couldn't find the lost mail in quarantine I agree it is most probably the AV causing the problem. I have switched off the AV mail check option and written a macro to perform daily back ups of my mail folders as a failsafe.

What AV program are you using?

And are you still running without problems with it turned off??