Windows 10 says you probably have an anti virus. Create an exclusion in that for the entire Thunderbird profile. IT should not be messing around with the mail files while you are trying to use them, but it probably is. They really are rubbish.

I added my entire Thunderbird profile folder to the exceptions for my antivirus but that didn't seem to make any difference.

Please post your crash IDsh

There's quite a bit actually, I'll post a few examples here:

bp-dc45ea55-08ce-4b79-91c4-c765c0181110

bp-52b1c48c-d708-409a-b010-d52e40181110

bp-8e023536-bb4d-4439-9860-dddf30181110

bp-b703cef4-0aa4-42c4-9d1e-cf2290181109

Let me know if you need more. Thanks!

Three of your four crash IDs is https://bugzilla.mozilla.org/show_bug.cgi?id=1333038 which is fixed in the newest beta. You can test it using https://www.thunderbird.net/en-US/channel/

AFAICT nothing in these crashes points to maildir

Sorry, no luck. Upgraded to the beta and still crashed. Here's the ID:

bp-17cf0b26-a3e9-406d-8937-106850181111

I'll be downgrading back to the previous build since several of my add-ons don't seem to be compatible with the beta version. Thanks!

And unfortunately bp-17cf0b26-a3e9-406d-8937-106850181111 isn't very helpful.

But thank you.

Could it simply be due to the large number of messages? Maybe a limitation of the 32-bit software?

Thunderbird being 32bit has no practical impact on how many messages are addressable. But good to see you are thinking :)

Hmm...so I wonder why this only happens with a maildir account but mbox is much more stable...

Borgholio said

Hmm...so I wonder why this only happens with a maildir account but mbox is much more stable...

I have a single maildir account in Thunderbird 60. It is really only read only, but it does not crash. There are 138,00+ messages in the all mail folder of the account, so really I do not think number of messages is an issue.

Are you able to repair the folder without any errors? The crashing usually happens when I am repairing a folder or moving a large number of messages.

Borgholio said

Are you able to repair the folder without any errors?

Yes

But why are you repairing folders? If the MSF iles is getting out of sync that usually indicate other problems and they might be causing your crash situation.

I would suggest you check the actual drive with chkdsk for physical or logical errors. It might be the crash is a sympton of issues with the storage media.

Whenever Thunderbird crashes in the middle of moving emails from one folder to another, it frequently corrupts the MSF file and forces me to repair it. If the folder is too big, it crashes while in the middle of the repair process and becomes stuck in that loop. So I wouldn't have to repair folders if it didn't keep crashing.  :-/

So since yesterday I tried Thunderbird in safe mode and disabled hardware acceleration, but no dice. Also tried Compatibility mode for Windows XP and 7 to no effect. Ran as administrator and completely disabled my antivirus. Chkdisk shows no errors on the drive. I'm not sure what else to try aside from replicating my mail accounts on another computer and copying the folders over. Anybody have any other thoughts?

Here are the most recent crash reports, if anybody is curious.

bp-155df7ac-88bd-4f2b-ad3b-f8b600181113

bp-96f8b459-c92d-4bbd-aad2-4d10f0181113

You really shouldn't mess with compatibility mode.

The first crash should be fixed in beta. The second doesn't yet have a patch

Sorry I don't have a solution, or even a cause. Try reseating hardware but I doubt it will help. I think you don't have a hardware problem