The problem with carrier pigeons is you gotta' clean up after them and feed them. My guess is this is a POP account and the popstat.dat file became corrupted, causing the download you are experiencing. Something you might try would be to create filter by date, moving to trash if prior to a specific date.

You might want to try https://addons.thunderbird.net/en-US/thunderbird/addon/removedupes/

It sounds like you have enabled "keep messages on server" in Thunderbird pop account settings. Not a great idea.

Back up your profile and turn that stuff off.

Wayne; Thanks for the suggestion, BUT the original question, went something like-"If I go to Thunderbird email "inbox", and select ANY message, it becomes "high lighted" in BLUE. I can then select [left mouse] to delete said message, and it gets sent to "TRASH" folder. Later on, I can select "TRASH" , and by "RIGHT" clicking get a drop down that says "EMPTY" trash folder. Which I do. Thunder bird suggested, that after selecting a message & highlighting it, I should press the "Ctrl & A" key at the SAME time. This high lights the entire page. Support then says to press the "Delete" key. Question?? If I depress the "Delete" key, will I JUST delete the messages showing on the screen, OR will it delete EVERY email in the Thunderbird in box?? First option would be fine but NOT the second. Thanks for your time, guess I'll use the "old" fashioned way of deleting 1 at a time. Then I'll just have to wait about 5 years, until I get another 1000 emails at once, from years past. Of course I may beat them to the punch, and be gone myself.-Joel