Do you use a POP mail account ?

If yes, then it sounds like the 'popstate.dat' file has gone awol. When you download mail using a pop account a record is kept in the 'popstate.dat' file. So when you access server again, the pop account knows what you previously downloaded and does not do it again. In your case, this has failed, so the pop account has something gone wrong with it's popstate.dat file.

I would bet that you have a new empty popstate.dat file and therefore when it accesses server Inbox, it starts to download whatever is in the Inbox.

It also sounds like you have selected the option to 'Leave messages on server' hence why you have the ability to download again. I'm not sure if you have also selected keep until you delete them and also compact your Inbox, Drafts, and Junk on a regular basis, but it would be adviseable.

Quick method to stop a major download:

• Logon to webmail account via a browser.
• Delete any emails that are still stored which you do not need to keep.
• Empty the Spam folder and the Trash Folder.
• For Emails you want to keep but do not want to download, create a new folder and move the emails from the Inbox into that folder.

Then you can start Thunderbird. Pop accounts can only access and download from server Inbox, if you have moved them out of server Inbox they cannot get downloaded.

What caused popstate.dat to go awol ? Possibilities like a computer shutdown whilst the file was open could corrupt it, an Anti-Virus/malware program scanned the file and messed it up or put it into quarrantine or some cleanup software like CCleaner or WiseCleaner thought it was a temp file and deleted it. File was corrupted so Thunderbird had to create a new one.

I would advise that you do not allow any product with 'cleanup files' capabilities any access to the Thunderbird profie folders as they have a habit of removing session, password, cache etc which in Thunderbird may not be desirable.

Thanks for the response. You're right... I leave messages on the server until I back up my whole computer and sometimes I forget to go back and delete them. Lessons learned!! I do use CCleaner and Avast and will make exemption for Tbird. Someone on another forum suggested that I removed the Popstate.dat file because it's corrupt. I'm afraid to mess with that. I'll try your instructions first. Thanks.

Okay, I got it to stop loading old emails but now I'm trying to delete the duplicates. Have an add-on called "Remove duplicate messages" and it did remove about 40 messages and stopped. There are still 700+ left to be deleted.  :-( Are there any other programs or add-ons that remove duplicate emails? I did a Google search but can't find anything but this one.  ????