Sometimes when this happens its Avast scanning. Disabling doesn't always make everything disabled and unlinked.

Folders are single files and you moving something into one will make the entire file be scanned. The folder that has the message to start with, will get a "to be deleted"-tag but that changes it and it might get scanned.

So make an exception in Avast for your entire profile. Compact your folders (that way all "to be deleted" - messages will be excluded.)

Another reason, if your moving from a folder to a imap-folder is that your connection is poor.

And then its Window 10 with its mysterious freezes

As a computer tech, I have never encountered a situation where an antivirus program still did real-time scanning when it was disabled. So I find it difficult to believe you.

To be thorough, I suppose I will have to do what you say, even though it will leave my computer open to infection via e-mail. Avast is currently blocking infections from my e-mail almost daily (almost entirely from spam). Since the freeze-ups occur intermittently, I will have to wait a long time to see if this will work or not.

As I said, the freeze-ups occur even when moving messages from one Local Folder to another, which is why I ruled out IMAP delays.

You don't have to disable your AV - just exclude the TB profile folder from AV scanning (that's different from unchecking 'Allow antivirus clients to quarantine...'). The AV will still protect you with its real-time background scanner.

Also, if you test with a new profile, see how it performs with a minimal setup (one account, no add-ons) before you copy over all the mail and contacts from the old profile.

- First, try disabling Allow Windows Search to search messages in Tools > Options > Advanced panel > General tab.

- If that does not help, try disabling Search Indexing in Windows, also known as Indexing Options. See here for more info.

Could you report back?

sfhowes said

You don't have to disable your AV - just exclude the TB profile folder from AV scanning (that's different from unchecking 'Allow antivirus clients to quarantine...'). The AV will still protect you with its real-time background scanner. Also, if you test with a new profile, see how it performs with a minimal setup (one account, no add-ons) before you copy over all the mail and contacts from the old profile.

I understand, sfhowes. I have excluded my Thunderbird profile and need more time to see if the freeze-up will happen or not because of this. My point is that I completely disable the AV for testing, and the Thunderbird freeze-up still happened, so I doubt that excluding my Thunderbird profile will result in anything better. But I have, just to be thorough in my testing, not because I believe your theory.

I understand testing a new profile without copying anything data to it. Unfortunately, real life makes that difficult. Especially when this issue deals with moving messages around, particularly within Local Folders.

I thank you for trying to help.

Tonnes said

- First, try disabling Allow Windows Search to search messages in Tools > Options > Advanced panel > General tab. - If that does not help, try disabling Search Indexing in Windows, also known as Indexing Options. See here for more info. Could you report back?

Thank you Tonnes, that makes sense. I have unchecked "Allow Windows Search to search messages". To disable Window Search Indexing is a drastic measure that I hope I can avoid, and really, I should not have to do.

Between these different things (Windows search, and Avast Pro Antivirus), I hope I can pinpoint the problem, and submit the bug to either Mozilla or Avast.

If it is due to Windows Search, then I will have to exclude my Thunderbird profile from Windows Search.

I will indeed report back my results. Since the freeze-ups are intermittent, it may take several days to narrow down a particular solution. Sigh. Like any computer tech (or anyone, I suppose), I hate intermittent problems.

Tonnes said

- First, try disabling Allow Windows Search to search messages in Tools > Options > Advanced panel > General tab.

That was it. Thank you! Too bad I had forgotten this in the two years since I last solved the same problem. I hadn't even remember that time until I saw it in my list of questions here. I will remember now!

Another user bitten on Windows 10 :(

FYI - the indexing and other ideas are listed in https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

Bruce A. Johnson said

Tonnes said

- First, try disabling Allow Windows Search to search messages in Tools > Options > Advanced panel > General tab.

That was it. Thank you! Too bad I had forgotten this in the two years since I last solved the same problem. I hadn't even remember that time until I saw it in my list of questions here. I will remember now!

You may be pleased to know that the option to enable this feature is being removed from the startup prompt for new users/new profiles, who often enable it not knowing what it will do for them, nor the performance impact.

So we hope to have fewer footguns in this area in the future.

Bruce, do you remember how or why you enabled the feature in the first place?

(and here is your long lost posting on this subject https://support.mozilla.org/en-US/questions/1033167 )