Lets start way back here.

Thunderbird is multi process. I have five process running at the moment. So two is not unusual.

You are running windows 9 which has a very heavy presence of antivirus activity from third party antivirus products to cover for the lack of support from Microsoft. Unless you have specifically excluded the Thunderbird profile folders from scanning the scanner is more likely to cause issues than fix them.

Compacting is best left for the system to do when it is needed. But a couple of issues here. Thunderbird does not flag aborting as an issue when compacting unless it is in the process of renaming the existing file. (and that is exceedingly fast part of the process. The compact works by creating a new "compacted" file. Once the file has been created the existing folder file is deleted and the new one is renamed to replace the deleted copy. Sometime these files appear in the folder pane as NSTMP folders when Thunderbird is closed mid compact as a backup in case the shutdown did in fact loose something from the original folder.

Thunderbird reporting it is busy is more likely to be updating the global index or processing the most recent download, running filters etc. Seeing busy error is often a clue the system is too slow, has a cramped hard disk or a lack of memory. Despite published minimums (which are patently absurd). Thunderbird really needs 2Gb of memory and more than 4 to function as designed and free hard disk space of at least the size of the largest folder (be that a 10Gb all mail folder from gmail or something else)

Standard operating procedure for as long as I have been using Thunderbird has been to to right click a folder, select properties and then the repair button any time message are not shown as expected. I suggest you try that now and see if it is an indexing issue.

Hi Matt,

Thank you for responding so fast.

Yeah, now I see that Thunderbird has two processes running and it doesn't show that it's busy doing anything (except checking to see if there's Email on the server every couple minutes).

I tried to "Repair" the folder earlier and the messages didn't come back. I just tried it again after you mentioned it- it did not help.

I looked for an NSTMP folder and there was an empty one (at the top/root Mail folder level) last modified 8/23/2022. Nothing else I could find.

I opened up the "Inbox" mail data file in NotePad and searched around. I found only the Email messages that were present-before and arrived-after I lost the 100 messages.

One thing I remember which could be significant: After the 100 messages finished downloading, I clicked on the "Inbox" (to view the contents of the inbox): Thunderbird had to rebuild the folder (MSF file I'm guessing) before it could show me the contents. It took some time to load (maybe 10-20 seconds).

When the Email messages are downloaded, are they immediately appended to the "Inbox" mail data file while at the same time the Inbox.msf file is updated? If so, under what circumstances would it need to rebuild the Inbox.msf file before showing me the contents of the Inbox?

• Maybe corruption occurred during the download; causing the Inbox & Inbox.msf files to get out of sync? How could that happen?

I'm guessing when these two files are out of sync the Inbox contents can't be viewed and Thunderbird automatically "Repairs" the Inbox. And if circumstances were right, it could rebuild the "Inbox" without all the newly downloaded Emails?

Or is there someplace else the newly downloaded Email messages could be?

thanks again! Jim

So I do not need to edit ever response just to read it. Please forget what they taught you in school and do not indent the first line of a paragraph.

Thunderbird appends each mail as it arrives so one of two of etc. the repair function simply blows away the MSF (except a little more gently that simply deleting the file as some data like tags for servers that do not support them is salvaged.)

If you have had the underlying MBOX file open in Notepad that there is nothing there, then nothing will recover them in Thunderbird, they are not there. The rebuilt MSF file on access could signify that the original was unavailable. This can see multiple MSF files with a number in the name created and never accessed again.

You might check, like with the MSF file that the inbox file is not having a copy with a number attached.

What size was the nstmp file you found? How did you determine it was empty?

Hi Matt, Sorry about the formatting issues. I couldn't figure out what was causing my responses to have a "scroll bar" in them. Thanks for the suggestion, I hope this looks better now.

There are not multiple MSF files with a number in the name. Just one: "inbox.msf"...

I guess I have to accept that the Emails are gone. Luckly I glanced through them on the server and I saw a few of the important messages. I'll contact the senders.

I'm thinking its probably best to set Thunderbird to "leave Email messages on the server" for at least 1 to 2 days just in case something like this ever happens again.

The nstmp file was empty when I viewed it on Thunderbird and it had a size of 0KB when I looked at it in Windows Explorer. I deleted it using Thunderbird.

Note: Normally I use Thunderbird on a Windows 10 Pro desktop. We were evacuated due to wildfire so I installed Thunderbird on my Windows 7 Pro laptop using the profile I copied from my Desktop. With the exception of this issue, it's been working great.

Final Questions: 1. Any idea how this could have happened and what I can do to prevent this from happening in the future? Could Windows 7 Pro be the culprit due to the anti-virus activity? (per your first message: no I did not exclude Thunderbird files from the scanning).

2. Like I said in my original post: I recently migrated from SeaMonkey to Thunderbird. I never had problems like this with SeaMonkey. Is one known to be more reliable than the other?

OR maybe this was an unlikely occurrence; and the circumstances that caused this issue would be hard to duplicate? I hope!

Thank you very much for your fast responses, sharing your insight and knowledge, and all of your time spent helping me! Take care, Jim