That setting is in account settings>copies&folders. I suggest changing the settings and then changing back. make sure the two accounts' names are sufficiently different so that you are assigning correctly.

I found out what happened...when I deleted the email account it was the default account so thunderbird assigned it to a different account and when I reentered the old email account it was not the default so it used the other account that was the default.

I changed the default to the correct account and the problem is solved. Terry