Here is more information. I had a problem with very slow mail deletion. I appended to this thread: https://connect.mozilla.org/t5/discussions/thunderbird-extremely-slow-deleting-emails/m-p/64427#M22685 . The solution in that thread did not resolve my problem. Then, a few days later, the problem vanished. I did not consciously make any changes that would have resolved the problem. So, in this case, I have no idea what inside the Windows 10 system was causing the problem and what fixed it. There is a possibility, I believe (from my many years of IT experience), that the same thing might be happening here. But I have very limit4ed knowledge of the internals of Thunderbird.

Has anyone seen this? I have not seen a response, and it is a BIG problem for me.

A workaround: https://bugzilla.mozilla.org/show_bug.cgi?id=1908761#c5

Thanks for the information. I looked at that bug, and there was a lot of dialog. I did not see a workaround, nor did I see the release in which the bug was fixed. A comment 4 days ago says "approved for Beta". So I assume that a fix will be coming soon. At one point I was running the nightly builds, but i prefer not to do that. If there is a workaround, I can try that, but I did not see it in the dialog.

The link gives the steps to eliminate the slow filtering, and is confirmed in e.g. comments 13 and 14.

The link gives the steps to eliminate the slow filtering, and is confirmed in e.g. comments 13 and 14.

Indeed exactly that - comment 5

Wayne, in my case the columns are "thread", Subject, Correspondent, and Date. The inbox is sorted by Date. I have 86,000 messages in my in-box. (I am on many candidate mailing lists, and they all want donations, multiple times per day). I usually delete them in bulk, by sender, but the current problem makes that hard. I never know/remember if I have "threads" enabled., and I do not know if that is germane to the current problem. This morning I clicked on the "threads" icon, and it appeared that the process was much faster. I saw mail grouped by threads, so I must have enabled it. Then I added the "Order Received" column. I sorted by that and then by date, and the process seemed to be the same duration as it was before I added the "Order Received" column. As a test I just clicked on the "threads" icon (turned it off), and a search for mail was slow. I then enabled "threads", and did the same search. It was faster. So, it appears that "threads" is involved somehow. Adding the extra column seems not to have made any difference. Now I would like to remove that new "Order Received" column, but I have not had time to look to see how to do it. I would like to remove it and see if I can duplicate my results with the "threads" setting. Thanks.

I just ran a test. I removed the "Order Received" column, and I turned off "threads" . I did a search "lgb" on my mail messages, and it took a while. The "X" in the upper right corner turned red during the search (i.e., not responding). Then I cleared the search and enabled "threads". When I did the same "lgb" search, it took much less time, and the Thunderbird process did not go into a non-responsive state. This proves (to me) that "threads" is somehow involved in the slowness. I might have expected that enabling "threads" would have slowed the process due to the extra work in combining the messages in each thread. But that appears not to be the case. I have not looked at the bug page to see if "threads" is mentioned.

Indeed, threading alone does not force sorting, and the performance issue is caused by sorting.

Note, unfortunately (AIUI), removing a column does not remove it's sort setting.

Wayne, thanks for the information. Is there a projected release when this bug fix will appear?

I'm hoping 128.2.0 within a couple weeks.

I'm hoping 128.2.0 within a couple weeks.

That did not fix it for me and neither did 128.4.0. See my remarks here