Seeing a screenshot of the account folders within the imapmail and mail folders may help. Sometimes, compacting fails and leaves detritus that can be readily removed. I make that request because my inference is that the large disk usage is due to the accounts,

Thanks - see below.

In one of the "Completed Emails.sbd folders there is one file - nstmp-1 - which is 657.1Gb.

What the hell is this, and what is it doing here?

nstmp files are the detritus remains of an attempted compaction that failed. Just delete. I was anticipating this. If you have very large message folders, this may happen periodically,

Brilliant, thanks David. I've now got a hard drive with enough space on it to start work again.

You're very welcome. :)

Err, not quite sorted, I'm afraid. I deleted that massive file as you advised.

I left my PC on to do some shopping, and when I got back, there was another file in another nearby folder of about 600+Gb and I was getting "low memory" warnings again. I've just checked again, and that same file (in the Employment folder) is clicking ever upwards in size - it's got to 240Gb as I write.

How do I kill these damned things permanently? Is there something going wrong with T'bird's compacting routine?

Thanks in anticpation.

I don't know the inner technical aspects of Thunderbird, so it's possible there is a bug somewhere, but my guess is you may have an antivirus product that is interfering with compacting. My suggestion is to adjust the Disk Space parameters in Settings>general, and possibly tick to be informed when TB is about to compact.

@tim292, what version are you running?

@tim292 Turn off automatic compaction for that account as a temporary workaround. This is a known bug that is actively being worked on - I had a multi-terabyte nsmtp file 😁

Wayne, V 125.0.

Lemonskunnk, I'm amazed that you reckon it's a known bug as I've found nothing to say that despite hours spent searching solutions. A link to that debate would be really helpful.

I've flagged it also with the PCLinuxOS forum.

Wayne, V 125.0. Lemonskunnk, I'm amazed that you reckon it's a known bug as I've found nothing to say that despite hours spent searching solutions. A link to that debate would be really helpful.

I am well acquainted with many issues.

https://bugzilla.mozilla.org/show_bug.cgi?id=1878541

Anyway, you should get off 125, and on to beta - 125 is a beta, but without the benefits of frequent fixes that beta has.

https://www.thunderbird.net/en-US/download/beta/

Thanks for the advice about moving off 125.0 Wayne. Unfortunately, that's the one in my Linux version repository, and, as the background structure of the application has (apparently) changed, I can't backtrack to an earlier version that worked. (I don't know why it was let into the repository in the first place, but that decision is above my pay grade).

I'll just have to leave off Auto/Any Compaction until a fixed version comes along.

The sooner the better!