(using T-Bird 38.7.1 on Win7 and XP)

Are you sharing the same profile on there?

Not sure what you mean. Two separate computers with the same account set ups and the same email addresses for identities. I get messages at the office during the day, copy the necessary ones into a "buffer" folder, copy that folder onto a thumb drive and then load that folder with the newer messages into Local Folders when I get home. When I then open T-bird at home, the newer version of that folder is there with the transported messages and I move them into their respective other folders at the house. (I do leave some messages in the buffer folder for future reference on things.)

Having moved out some larger messages, the folder may need compacting. I have done this. And sometimes the messages remaining - all of them! - disappear. Sometimes not. I have not been able to discern what factors are in play with this disappearing act takes place. Can see no rhyme nor reason for it. That's why I came here.

My system right now is to manually backup all folders before I hit anything that resembles compacting.

How do you do all this loading and unloading of your buffer folder?

I'm not saying this is definitely part of your problem, but it is an unconventional workflow. Most of us use an IMAP-connected account where we need to work with messages in two or more locations, or via two or more different devices.

I've never tried moving material around in the manner you describe, so I can't help but think that's part of your problem.

Email clients are designed to work with email servers. Any other form of import/export is a kind of bonus feature, and not anticipated to be used as a principal means of transferring data. If I were copying large amounts of data in and out, or doing a lot of compacting, I'd be inclined to take Thunderbird off-line for the duration.

"How do you do all this loading and unloading of your buffer folder?"

There is a folder on both computers call Buffer. If there are any emails that come into the office and I want to take them home with me, I copy them into Buffer. At the end of the day, I copy that folder (from within the Profiles tree under User) to a thumb drive. The original folder stays on the office computer, but a copy is on my portable drive. When I get home, I move that folder copy into Local Folders under the home identity. It replaces whatever was there on the home computer with the transferred office Buffer folder. When I open up T-Bird, that Buffer folder is now the version I just transferred from the office and I can move the emails into their respective folders on the home machine. I now have emails on both the office computer AND on the home computer that came in while I was at the office.

This system worked for years with Outlook Express and works from time to time with T-bird. It's just that sometimes after compacting that Buffer folder, all the emails disappear...and sometimes they don't.

Makes sense? "Cuz if you have another way now that I'm using T-Bird, I'd be willing to listen.

ps....The two machines are not networked and there are no plans to do that.

The Thunderbird profile is hidden. You've had to undo that to be able to use your idiosyncratic method. That's a bit like disabling the safety interlocks on a dangerous machine simply because they are inconvenient, without stopping to ask why they are there in the first place.

You drop onto your unsuspecting Thunderbird a changed folder. Whatever index it had for that folder is now obsolete. At the very least, I'd delete the associated msf file when copying in the buffer file, obliging Thunderbird to re-index and take stock of the changes. Compacting will go awry if the index is out of date. I do hope Thunderbird is closed down while you're performing open-heart surgery on its data?

If I had to use such a technique, I'd consider swapping the whole profile, or at least the entire branch of the affected mailstore (hint: look at the "Local directory" setting under Account Settings|Server Settings). Or I'd use the ImportExportTools add-on to formalize the process of copying in or out a specific folder. And after importing, I'd open Thunderbird, and I'd right-click the transplanted folder, select its Properties and "repair" (i.e. re-index) it.

I don't get having email and not being "networked". Email is all about networks. That one called "the Internet" in particular. You have two computers with email clients. Email is all about communication between disparate devices and you're choosing to shuffle your data about manually. I can't think of any word to describe this other than "perverse".

Do you understand what IMAP has to offer?

I'll try deleting the MSF and/or let it rebuild/repair itself as another option.

[I don't get having email and not being "networked".] My home computer does not connect to the office and vice versa. I have no intention of doing that. And I see no benefit up to this point of leaving messages on the server until I go into the server's email interface and deleting everything.

Thanks for the suggestions.

The benefit is that you use email as it's designed to be used; communication using standardized protocols between client and server.

Not fiddling in an ad-hoc way with its internal storage mechanism ignoring any interdependencies you may not even be aware of.

Why would you have to go to a webmail interface? Please learn about IMAP.

You could set up a separate IMAP-based account just for the messages you want to take home. Copy them into this account at work, there they are waiting for you at home. Move them to Local Folders (where you keep everything else) when they don't need to be circulated any longer. You do this all as simple, legitimate operations within the email client, rather than tinkering under its hood.

I just can't come up with any polite words for this awful horrible practice you have got into whereby you open hidden folders and copy arbitrary contents to and fro. It's like using a hammer to put in screws, or using a chisel to undo the screws. It's just wrong.

Zenos said

I can't think of any word to describe this other than "perverse".

We used to call it a sneakernet

Fred_B said

[I don't get having email and not being "networked".] My home computer does not connect to the office and vice versa.

The internet IS a network, a huge Network, a Network of Networks even So your computers are networked.

I think you need to seriously look at IMAP for managing your mail. Your comments make it very clear you have no understanding of IMAP as a protocol and are stuck in a sneakernet using POP and fighting to stay there.

Read about IMAP. here for a very short summary. https://support.mozilla.org/en-US/kb/glossary-terms-including-types-accounts#w_imap

IMAP synchronizes folders and mail between the server and your computer or computers. so automatically anything in one is in the other. mark it read on one it is marked as read on the other. Delete it in one and it is delete in the other.

Move it from the mail servers folders to a local folder and you effectively delete the mail from the server and other devices.

The primary concern is if your mail provider actually supports IMAP. Most do as it is also ideal for use on phones and tablets. I personally use POP for my computer, simply because of the way I work and the fact I use it on one and only one device.

"So your computers are networked." Not if I don't establish one. I may be connected to a server to get emails and whatever, but I cannot go into my office computer from the home one nor vice versa. Therefore, as I see it, they are not networked. There may be some connection possibilities, but it is all done through some intermediary contrivance or service. I stand by my earlier comment.

As for what my serve will allow re: POP vs. IMAP (and I quote): "Clients that are hosted with us that use Thunderbird for their email client need to make sure that their server setting is using POP instead of IMAP." And I understand as much as I need to about IMAP for a system or protocol that is not pertinent to my situation.

As for the rest of this geekitude and condescension that seems to hold court, thanks for nothing. I asked for some nominal assistance on a specific problem and not a wad of pedantry.

For someone doing things way outside the acceptable you sure are testy.

You are basically hacking Thunderbird and getting upsett that it dies not like it.

You are using a protocol that is inappropriate for your needs based of what looks to me the advice of someone is still stuck in the 1990s offering only POP.

But you are right. You do whatever you like and I will go away and let you do it. But do not ask for support in your hacking. like zenos I see the problem, and it is not Thunderbird.