Before you say you do not want this to happen you probably should learn what it is and that it is an essential part of maintaining your email system.

http://kb.mozillazine.org/Thunderbird_:_Tips_:_Compacting_Folders

More good reading.

http://kb.mozillazine.org/Keep_it_working_%28Thunderbird%29

If not the next question you are going to be posting is "I lost all my emails. how do I get them back?"

Do you understand that when you delete, it just hides the message from sight? And that compacting is necessary to delete permanently and recover the disk space that was occupied by the deleted message?

Maybe your trigger threshold for compaction is set too low?

My Question is WHY would I lose my email, only if someone that thinks! I'm smart takes them,or writes a program to do that 1) any I want, I save into a file on my comp, not in the email program 2) when I deleate at least once a week I delete the deleted files I donot use the deleted folder as storage ON my previous email I had it to empty the deleted folder on closing the program, more sence 3) This is a dusy about 10 or more yrs ago ! I compacted my email because my disk space was low, guess what! IT used up the space I had and locked my computer that I had to format the drive!! SO in my opinion compacting does not save disk space! ITS B S 4) I have read that your compactor slowes down the email program SO why is it in my face all the time Barry

From your answer you did not read the provided links and still do not get it. Maybe someone else has time to explain it again.