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from your writing it appears that you would like to disable auto-compression. As a precaution to protect your saved files so that in fact you feel safe about your already large number of folders over the years. This function can be activated without any problem and can be deactivated in our preferences menu.

Greetings Firefox volunteer

Hello there

Disabling your folders from automatic compression, on the other hand, means that deleting folders or messages may not be executed or they may leave messages from your folders undeleted. If you do not use them, this will not hinder you, of course.

The options Preferences (formerly Options) > Network & Disk Space > Disk Space

the options will get you there To configure that subject.

https://support.mozilla.org/en-US/kb/compacting-folders

At most, Thunderbird scans the files that are Mbox related to your subfolders below, this subfolder will also have to adhere to these in order to be recognized as this.

When compressing folders there are always clear questions as to whether these actions are actually performed and whether these steps could pose a risk of loss also when using add-ons or tools for this purpose

https://addons.thunderbird.net/en-us/thunderbird/addon/xpunge/

Especially with large quantities, I would increase alertness. And don't take unnecessary steps. And take a venture to backup this before.

Greetings Firefox volunteer.

I have noticed that in the latest Thunderbird version (I'm using 115.6.1) the Compact folder starts automatically compacting all subfolders under the current one.

I don't think I'm seeing this here, but I'm not quite sure about it. The only indication of compacting action happening is in the status bar. Do you have any other method to determine which folder(s) are actually being compacted?

Those folders are "read only" (I only have them for reference), and I do not want to modify them in any way, to avoid risking their contents.

If those folders don't change, then why do you think Thunderbird would compact them again and again, even if no disk space can be recovered from compacting?

The best protection against data loss is to have a recent backup of your Thunderbird profile. Data loss can also happen for other reasons than failure during compacting. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile

I do have the automatic compaction turned off. I have always had it that way. What I'm talking here is about manually compacting folders via the folders panel context menu.

I know Thunderbird is trying to compact subfolders because of the status bar message. I have been able to stop it, but I do not want to play those tricks or risking committing a mistake in the future. Maybe some of the old folders aren't compacted, but, as I said in my original post, I consider them read-only and do not want them to be modified in any way. And, anyway, I have not found a way of stop compacting short of closing Thunderbird (and comparing the affected files with the profile backup, see bellow), which is too risky for archive material, and do not want to rely on always remembering I have to do that.

What I'm asking for is a way to control the compaction, in a way that it only applies to selected folders, or at least excludes the "archive" ones. A best practice in data preservation is not modifying it unless it's absolutely necessary, if at all.

I do have a complete up-to-date backup of my Thunderbird profile, which currently weights in about 24 GB. The backup is in a separate hard drive, and it is updated daily. So you can see that I do take the possibility of data loss very seriously. The profile contains all my mail since 2000, back when I used Netscape Communicator, thanks to the backwards compatibility of the mailbox file format.

Since the dawn of time, the Compact folder command on the folder context menu has compacted just the selected folder. However, I have noticed that in the latest Thunderbird version (I'm using 115.6.1) the Compact folder starts automatically compacting all subfolders under the current one. This is a big problem for me: under the inbox, which I need to compact fairly often because all messages pass through it, I have literally hundreds of subfolders, some of them dating from more than 20 years ago, when I used Netscape Communicator. Those folders are "read only" (I only have them for reference), and I do not want to modify them in any way, to avoid risking their contents. Thus, I DO NEED for Thunderbird to stop compacting subfolders automatically. Is it possible? How can it be done?

I tested a daily development build with fastmail, but I did not test version 115:

• An Inbox that has subfolders, and I am not able to reproduce this.
• A non-Inbox folder with subfolders, and I am not able to reproduce this.

Also, after a folder compacting has started, what's the best way of cancelling it, short of closing Thunderbird?

You cannot cancel.

Even if the compact issue gets resolved, I cannot recommend setting folders to read-only. It is not supported, so no guarantees you won't have other issues in the future.

Wayne Mery said

Even if the compact issue gets resolved, I cannot recommend setting folders to read-only. It is not supported, so no guarantees you won't have other issues in the future.

Note that I put "read only" between quotes. The files aren't physically marked as read only, it's just that I consider them as what they are, an archive, and thus I do want NOT to modify them. I know enough not to go around messing with file permissions without knowing what the effects would be.

That said, today I have tried to compact my inbox again (after making a backup of the profile, of course), and it hasn't tried to compact the subfolders. Of course, I haven't changed anything in Thunderbird's configuration (the only related setting, the automatic compaction, has always been disabled, as I said earlier). I sincerely do not know what's going on.

Not related to this Thunderbird problem, I see that the forum insists on putting the threads I open in the Spanish language forum, even if when I open a thread all the UI is in English. I'm sorry for the inconvenience, but I don't know exactly what's the cause (maybe the browser's Accept-Language HTTP header?), or how to correct it.

Best if you post the last issue you cited in a new topic with a related topic title. Thx.