Hello there We have read the situation In most cases when using Hotmail/Outlook domains within Thunderbird, there will be no notification from the program to enable or disable certain topics for better use. In this case, place a copy of the sent message in the sent folder again. The issue that IMAP users having mostly. Having or getting these providers together it might that there is a another (double)copie of the message in that sended folder again. Account settings > copies and folders and change it to not save a copy there . That could change the complete situation.