I guess the move is still happening in the background and consuming all the available connection, so no new mail is coming in.

Each of those message will have to be uploaded to the internet, so you may find if it was a lot of messages, or they were very large that it might take more than one day. The upload bandwidth available is also a factor. Usually that is about 10% of the advertised download speed for consumer grade internet connections. (it is one of the limits providers use to justify changing a lot more for business class internet)

My recommendation is start Thunderbird without your antivirus product scanning emails as that may well have a significant impact on the success or failure of the activity.

Thanks for this info. I'm following your suggestion. I've turned anti-virus off, and I'm letting Thunderbird "be" in the background.

I would have just assumed that nothing's happening; I'm clearly not getting any new messages and nothing looks different just by looking at Thunderbird. But I have Task Manager running and there are occasional bursts of CPU use by Thunderbird and the memory that Thunderbird is using is shifting. When I started just letting Thunderbird sit, the memory usage was about 214 MB. I've watched it go down to 199 MB, then 185, then before I went to bed it was 121 MB. Now about halfway in to the second day, it was down to about 100 MB. Does this behavior sound like what you'd expect?

I would put those messages into a local folder instead of a server folder.

Rick --

Thanks for that tip. I've never really considered the difference between "Local Folders" and the others. But now that you've pointed this out, it makes a lot of sense to be aware of the difference. So I think you're saying that if I had simply moved all messages to a Local Folder, I would still have all of the messages, but Thunderbird would not have to maintain and copy each message from one location on the server to another. They would all just go to a location on my computer. Is this right?

And how will I know if/when Thunderbird is done? Right now, I can't see any apparent difference in Thunderbird. How can I tell if Thunderbird is just never going to come back??

Rick -- Thanks for that tip. I've never really considered the difference between "Local Folders" and the others. But now that you've pointed this out, it makes a lot of sense to be aware of the difference. So I think you're saying that if I had simply moved all messages to a Local Folder, I would still have all of the messages, but Thunderbird would not have to maintain and copy each message from one location on the server to another. They would all just go to a location on my computer. Is this right? And how will I know if/when Thunderbird is done? Right now, I can't see any apparent difference in Thunderbird. How can I tell if Thunderbird is just never going to come back??

Yes, that is correct. This approach avoids copying or moving messages among server folders, which takes much time and, some people have said, may be prone to errors.

First, make a back-up copy of your profile.

Then make sure that all the messages that you want to copy or move are downloaded from the server. I believe that the way to do that is to go into properties of the source folder (right click on the folder and select "Properties"), then click on the "Synchronization" tab, make sure that the the folder is selected for offline use and press "download now". If all your messages were not already on your computer, they should be soon.

Then create a local folder.

Now I would go offline so no new messages arrive during this process. Select all the messages in the source folder. Right click on them and select "copy" them (not move, in case something goes wrong) to the local folder. They should all be copied fairly quickly. I just copied 2,000 messages in a few seconds. You can tell when the process is done by comparing message counts in the source and destination folders. You can also see entries in the Activity Manager (Tools menu) and maybe progress in the status bar at the bottom of Thunderbird's window.

Now you can go back online and delete the messages in source folder. If you use the standard delete function, they will still have to be moved to the trash, so there will be a long move between server folders anyway, which you wanted to avoid. But you could use shift-delete to delete them immediately instead of putting them in the trash folder. That should avoid moves between server folders.

All this is describing what you could have done with your inbox and what you could do with Inbox 2025 now. I am not responding to your initial query. For the problems of Thunderbird crashing and not getting new messages, I would try the standard troubleshooting method: start Windows in safe mode with networking, then start Thunderbird in troubleshooting mode (help menu) and see if the problems persist. If they don't, you can start looking for the culprits. If they do, I probably cannot help anymore.