And asking the same question again in the same forum with the same volunteers is going to change the response you get how?

You said "t appears to me that thunderbird becomes unstable with large amounts of history. It may work well with small email accounts but for larger amounts of email it may not work well." https://support.mozilla.org/en-US/questions/1356952#answer-1457559

That is certainly the case if you do not have sufficient ram or are using a slow hard disk. I see no mention of that at all so far. But as a general rule you need more that 8Gb of ram is you want a large all mail folder to even consider functioning without sending the disk into overdrive paging memory and being about as slow as molasses pouring on a cold morning.

Please try the following and report on your result of each step.

• Restart Thunderbird in troubleshooting mode. On the Help menu, click on "Troubleshoot mode" and continue whin that mode when prompted. If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender. Note, that anti virus products can insert hidden addons. (nice hey)
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates or even a proxy.

If none of the above result in a good outcome please do the following?

1. Open the menu > Help > More Troubleshooting Information, then click Copy text to Clipboard.
2. Go to https://pastebin.com, paste the info from your Troubleshooting Information page, use the Create New Paste button to create a page containing your info, then copy the resulting URL (address) of the page created.
3. Open a reply to this post, and paste the link to your troubleshooting information you just copied. You could just try a direct paste into this forum, but often it runs into an issue of being more than the 1,000 line limit of the forum.

I am of the opinion that without detailed information such as the troubleshooting information supplies we have no hope of guessing what your issue is. I can say I have never heard of someone without the ability to change IMAP subscriptions.

Why do I ask the same question of the same volunteers and hope I get a different answer? Because I just did from you and it may lead me to a solution.

First, my system should be sufficient. While a few years old, it is still reasonably capable. The processor is an i7-8700K running at 3.7 GHz, 16 GB of RAM, and a high speed Flash drive as my OS disk (there is a separate RAID array for bulk storage). I am running 64 bit Win10.

I restarted TB in troubleshooting mode and one thing that I realized was that I have been using a unified inbox. For some reason this was hiding IMAP folders in Gmail. Turning this off in "normal" TB operation allows me to subscribe (or not) to my Gmail folders, including All Mail. I have a few email accounts but can have them all auto-forward to one to have essentially the same functionality so this bug or characteristic of TB isn't a big deal.

I will not know right away if emails are corrupted or not as it can take some time. The ones that were corrupted before are still corrupted. One thing I determined is that while TB appears to completely freeze (no UI response, "Not Responding" from Windows, etc), if I leave it long enough (usually about 45 seconds) the message will open and then be normal. This behavior is the same whether TB is started normally or in diagnostic mode. Upon further experimentation, it appears this is now only occurring in the inbox and one other specific folder (a very important one though). By the way, besides the unified inbox I have no add-ins or themes in TB.

I will check back in after a few days pass. In the meanwhile, if anyone has any idea how I can get the one slow folder to work properly I would appreciate it. I have of course tried repair and compact and neither had any effect. I also realized that the mail status messages do change and are active during the times the UI appears frozen so background processes are still running.

. I have of course tried repair and compact and neither had any effect. I also realized that the mail status messages do change and are active during the times the UI appears frozen so background processes are still running.

But did they actually occur. What you are describing sounds like one of two things.

• Your raid array is actually unable to cope with large files (each folder is a single file and may be 10's of GB in size.) if your storage system is remote that just makes things even more unlikely to be stable. My experiences with consumer level raid arrays is not good. Especially the garbage sold by Dell.

• You anti virus is actually messing in the profile folder while Thunderbird is trying to do it's thing. Nothing like file contention to kill things.

Some general things to do and check; Disable on access scanning in any malware or anti virus, Disable any streaming backups of the folder or cloud synchronization. Disable windows search indexing of the profile folder. Open the profile folder in the windows file explorer. Locate the relevant inbox file for the account you are having issues with. (imap mail or mail folders contains IMAP and pop accounts respectively.) Mail is then in sub folders named for the mail server used. Check the file date and time details and compact. Post a successful compact, the file will have a new creation date. Did it complete successfully or did it leave an NSTmp file behind?

My profiles are on the fast SSD which is local. It is a server grade device and I copy very large files between that and external drives all the time without issue (plenty of free space). My system was built by a custom shop which did corporate workstation builds where I had worked. Couldn't stomach the quality level of Dell consumer stuff. Although not applicable here, the RAID uses server drives not consumer crap and is rock solid.

I have blocked Malwarebytes from scanning the profile folder. I do have a streaming backup (IDrive) but am somewhat hesitant to lose my ability to automatically backup my email. Besides, it only runs at night after I close TB. I already have Windows indexing off.

I do see the datetime change on the INBOX folder in my profile to when I did the repair and compact. There are no NSTmp files to be seen.

The problem remains.

Summary: I have disabled virus scanning and all indexing or backup of anything relating to TB. I have turned off unified inbox.

Some (but not all) incoming emails have huge amounts of garbage appended, which looks like: > ���qƫzYh�� q�`��� > Ģ�v�����Ƭ�����zV�y��zV�y�q�`��q�`���)���슉߮��jצz��蝲��y�m���h�\��vIFg��^sa������xI�^�,\�l� > � RJ)���*�i�"ά1`�P)����^w�ޕ�^u�{]4��lm�Mu��i��Ơz�Z�颙�ޮȨ���֭zg�����.n7�������;�)wd�f|���6ށk�8>��u�2��0&��)B�o�1��2�1&���
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Update: All of my problems are indeed due to actual Thunderbird bugs in the latest beta versions. I am running on the release version 91 now and all seems well.