For the Profile backup, what matters is that all the files in the Profile folder get backed up.

I don't know how MozBackup backs up things. Since it is not supported anymore and causes problems, I don't see any point in me learning about it.

The point in creating a new Profile is to not just reinstate the old Profile, which MozBackup might do.

I agree that creating a new profile and importing stuff from the old profile is daunting. Unfortunately sometimes that's the only way to fix what is going on.

Keep in mind that I said to create a new Profile to test first to see if it works better.

Understood Bruce.

Thanks.

Here's a potentially significant wrinkle...

Sunday, after having run diskcheck Saturday night, my e-mails downloaded with only a few (~3) sorting failures... a real improvement.

Last night I did my bi-monthly computer backup which is preceded by running Enigma's RegHunter (which I run twice a week and only mention for completeness' sake as it's pretty clearly not involved) & CCleaner.

Today, my e-mail's sorting was terrible.

Is CCleaner deleting information needed for sorting? Is there something I should uncheck (see image)?

Note: I've used CCleaner every 2 weeks before backup for many years and this would have to be some kind of new event.

Have a look at my blog post from 2012 about that wonderful messer up of Thunderbird, that all started because folks could not keep the reading pane in the state they wanted it. It kept reverting to it's default state.

https://thunderbirdtweaks.blogspot.com.au/2012/06/thunderbird-and-ccleaner-or-my-settings.html

I recommend you don't allow it to delete anything, but in particular the cache is used to hold a "working set" of data for IMAP accounts and the session file it deletes contains Thunderbird user interface settings. Basically it assume Thunderbird is a browser and has no specialist functions beyond that.

Many thanks... will check it out & make appropriate changes in CCleaner's functions.

I agree with Matt about CCleaner and Thunderbird. Un-select everything for Thunderbird in CCleaner. I used to have it clean a couple of things in Thunderbird, but not anymore. I learned my lesson.

In follow up... After assiduously doing file repair and creating new filters for all messages that were not being properly sorted I downloaded (only - 120-150 being more normal) 71 e-mails today without a single sorting failure... no other interventions. As an aside; a coexistent issue of the 'mark as read' function being selective when I'd select all my folders to mark as 'read' causing me to have to review my folders and mark those not marked individually has also seemingly resolved.

We'll see...

Last F/U on this issue until it recurs; just downloaded 193 e-mails W/O single sorting error. There seems to be some kind of repeating but self-resolving 'glitch'.

I'm late to this topic which is exceedingly long. So a couple questions...

Do you still have a filtering problem, either consistent or inconsistent?

Thanks for asking Wayne. At present the issue remains in remission... have no idea for how long or what will restart it though...

Well, after about 3 months of absolutely trouble-free use; during which time I've been downloading as many as 350 e-mails every other day, I just had about 50% of my downloaded messages fail to sort to files they'd sorted to yesterday. Again, same error message (attached). To my knowledge, there've been no TB updates installed, or any other events affecting my computer or its programs.

I don't know if this is a 'one-off' or the start of another truly annoying siege of difficulties.

Please review the prior suggestions, none of which worked, if you choose to respond.

Thanks.

Couple days ago I had a situation where all messages were not filtered for about 20 minutes. It was shortly after after I switched laptop power modes a few times, the last one was from lower power mode to normal.

Thanks for the input Wayne, I'll see tomorrow (when I intend to download mail again) whether or not the issue persists... sadly though, I expect it will if history is any predictor of the future.