Hello! mustan. Thanks for the details.
Outlook could be creating its own copy of sent items. So you need to check that.
- Open Outlook.
- Go to File → Account Settings → Account Settings.
- Select your Gmail account → click Change.
- Click More Settings → open the Folders tab.
- Choose: “Save sent items in the following folder on the server”
- Expand the Gmail folders list, then pick:
[Gmail]/Sent Mail - Click OK → Next → Finish → Close.
See if this helps. If you need further assistance, just let me know.
Best regards,
Kimberly