Thunderbird outlook hotmail messages appear twice in SENT-folder

How can I keep sent messages from appearing twice in the ” sent ” folder. I am using and e-mail addresses with IMAP.
Each time I send a message with Thunderbird the sent message is put in the “sent” folder two times.
What setting needs to be changed to in order to have only one copy of the message put in the “sent” folder?

The answer:
Outlook/Hotmail and gmail automatically put copies of sent mail in the imap sent folder. If you have settings to also keep a copy then two are being put in the sent folder.

right click on imap mail account in Folder Pane
select 'Settings'
select 'Copies & Folders'
in 'When sending messages, automatically:'
uncheck : 'Place a copy in:'
click OK

Solution was found here.
Have a nice day!