I can't see how to edit my post so here is additional info. All other folders work as they should.

re :What I have done: updated to latest T-Bird Compact the folder did nothing.

When you delete an email, it is marked as deleted and hidden from view, but at this point it is recoverable and so has not ben fully deleted. Compacting a folder means removing any emails that have been marked as deleted and hidden from view. You would not see any difference in the Folder Pane, but if emails were removed then the size of the folder would be reduced.

re :Properties\Repair Folder simply deleted all of the emails prior to 6-29-2020. Same with deleting the .msf file with T-Bird shutdown, and then starting T-Bird.

The 'Sent.msf' file is just an indexing file and does not hold emails. Repair Folder or deleting the Sent.msf file, means the 'Sent' mbox folder is checked and a new index file - Sent.msf - is created a fresh to show exactly what is in the 'Sent mbox file'. It does not delete emails. So it implies the emails were not in the file.

Check: Try the following to see if any of those emails has been 'marked as deleted'.

• Exit Thunderbird
• Access profile folder
• delete 'Sent' and 'Sent.msf'
• Copy backup 'Sent' mbox file from backup to account folder as before.
• Open the 'Sent' mbox file using a text editor such as Notepad++

The emails are stored in the order created, so the oldest will be at the top.

Look for the following line which is located near the start of each email.

• X-Mozilla-Status: (not X-Mozilla-Status2:)

X-Mozilla-Status: will have a number, please make sure the number says 0001.

• Work down through the document, use 'Edit > Find' - editing as required, making sure all emails have X-Mozilla-Status: 0001
• Save the file.

I've posted Images below to assist as a guide.

Do emails look intact, not just headers, can you see content ? Did you need to change any X-Mozilla-Status: numbers ?

Thanks for your response.

I went through the old and new Sent files and found that in the new one the 30 something emails Jun 29 to July 7 repeated over and over, but in the older Sent files they didn't, but they did have the gibberish coding for the attachments that I verified were actually attachments to some of the 30 something emails.

To answer your questions: all of the emails present had X-Mozilla-Status: 001 and all of the emails had content.

Bottom line is the older emails are simply gone and were gone prior to our attempt to recover. The GoodSync Backup is set to save only that last version, so all we had to work with was that day's Sent file, the day before Sent file, and the day before that Sent file, which were the same file size increasing a bit day to day.

Now the question is, how could the older emails have disappeared? If we can figure that out, then we can put in measures to keep it from happening again, as something similar with Sent happened in 2016.

Thanks for your help, Robert

I see a number of possible causes, but the reality is you may never know what happened.

I suggest you run a disk integrity scan using operating system tools. Often (especially as a platter or NAND ages errors creep in) these only become apparent when you can not read data that you think should be there.

I also suggest you might have some joy using the import export tools to try and import from your oldest backup. https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/?src=ss Do not restore the sent file to Thunderbird use the tools to try and import from the backup file. If it is not corrupt sent items should ensue. Assuming they are actually in the backup that is. It is not clear from your last response.

While you were editing in the sent file, were their message in there with dates before your apparent loss. I would assume their would be, as storage is oldest mails in the file first. So the first line in the file will be the date of he oldest message in the file.

Unfortunately there are occasions when entire file of mail disappears, but the common cause is perhaps the hardest to swallow. Anti virus product routinely advise they have found a nasty and offer to "clean it up" their usual approach is delete the file, or place it into a "quarantine". The result for Thunderbird is the same, it does not notice the missing file so the user interface still shows the old mail from the MSF store, and search still find them from the full text database it uses, but the actual email is no longer there. File size is not an indication here, as the last email added has an offset stored in the MSF, so when a new mail is to be added, it is and written to a location after the "last" email. So the first part of the file is actually empty space on occasions. Compact sure cleans that up.

You might have a chance of looking through any quarantined items from your anti virus product to see if there is a sent file in there somewhere.

So mitigation is to not allow anti virus products to scan the Thunderbird profile folder at all while the program is open and not allow automated repair following any detection in the profile folder. Just to be clear, email as rest in a file is text. it can do nothing malicious to you or your device. Even in Thunderbird there are no scripts run or external program launched, so opening even infected email is actually fairly low risk. Opening infected attachments is however another kettle of fish. But and this is the big but if you chose to open an attachment. First it has to be converted from text to it's original form, then written to the temp folder so the helper application associated with it can launch to load it. Any anti virus product should has started going nuts at the files appearance in memory and gone fully spare when it is written to the temp folder and at this point nothing has been launched, it just exists. So suggesting email scanning and profile scanning be disabled is not really asking you to expose yourself to risk

It is also a good idea to compact folders regularly as that "forces" a re-index so you miss things sooner. Early detection is often key in recovery. You certainly stand a better chance of a successful recovery from backup if bad backup have not had a chance to replace good ones.

Also don't forget to check the Versions in properties in windows file manager. I just did something like on my profiles archive file and it found a 2015 copy. That is not from my backup set, so I assume there was a shadow copy or restore point. But it is worth having a look.

Hi Matt, Sorry for the delay, but I have been swamped. I saved and printed your response and will try some of those things when I get time on the client's computer, but in the meantime, he can access those emails at AOL, so they aren't totally lost. I am going to mark the problem solved to close the thread. Thanks again for your help. Robert