How do I undo major changes such as filters and deleting filters
I recently was attempting to get a new filter to work, and tried many different options. When it did not work, I clicked an option I regret clicking called, "Match all messages." I clicked "run filter" and Thunderbird crashed. When I restarted it, it had indeed moved all of the thousands of messages in my main inbox to the folder I designated. I want to know how I can undo this? Does it involve just moving all those messages back to the inbox and deleting the filter?
Also, I accidentally deleted a filter I use a lot and consider important, and it took some fiddling to get it to work right. I can't remember exactly what I'd done to make it work. Can I simply undo this deletion or must I remake the filter? The "undo" option is grayed out and CTRL+Z doesn't work.
Opaite Mbohovái (7)
I have tried moving my messages back to the main inbox and Thunderbird crashed again--upon restarting it, I cannot find any of those messages in the filtered folder or the main inbox.
I can only guess that your anti-virus software did mess with Thunderbird mail files when you did move a large number of messages at once. As a result mail files are corrupted, and the visible effect usually is that messages disappear. See if this article helps. http://kb.mozillazine.org/Disappearing_mail
If not, restore a recent backup of your Thunderbird profile, which you hopefully did create before you started messing with the filters. That would also reverse the damage done to the filter settings.
Moambuepyre christ1 rupive
I unfortunately did not--I seem to have done irreparable damage to my emails now. I was only trying to filter out all the adverts I get that I don't necessarily think of as spam, but don't want mucking up my main inbox.
Moambuepyre ryanch1 rupive
I found the messages after repairing the destination folder in the filters, now I have to move nearly 10k emails, which makes Thunderbird crash. But at least I've found them.
On the toolbar 
> Help > troubleshooting information.
Please post the Crash Reports section of that page. (drag over it with your mouse and press Ctrl+C to copy) It would be interesting to put the issue in context with the actual crash report.
What anti virus do you use?
I use Windows Defender. The messages were not there, instead showing back up in Thunderbird later. I moved them back to the inbox which took a while.
I have only one crash report to post and it's from June. I guess what actually happened was that Thunderbird went into (not responding) mode and never recovered during these operations. Was it too much for Thunderbird?
MY guess as to what happened is.
You moved 10,000 messages. This probably means that a single file was opened for writing 10,000 times in very short order. Nothing intrinsically wrong with that.
That is until you bring idiot anti virus program to the table. So we now have defender trying to scan the file your opening 10,000 times every time it is opened. Unfortunately the last time I looked it takes an anti virus programs about 10 minutes per Gb to scan a file. The result is fairly obvious here. Something has to give. As Thunderbird is basically a single threaded application, something standing in as a road block will see everything stop until the road is again free.
So no, what you did is not to much for Thunderbird. But you might seriously consider placing an exception in Defender for your Thunderbird profile to prevent this sort of madness in the future.