Hi SylvieBotha,
Thank you for posting your issue on Microsoft Community Forum.
I'll be happy to help you with your issue that sent items are not showing in Sent folders. For us to isolate your issue, kindly verify if you have tried the troubleshooting steps given on this thread. If not, kindly try to do so as it may help you resolve the issue.
However, if not, kindly provide us the log files on the private message I created as we need it for our investigation. To collect log files, follow the steps on this link.
Please click on You have a private reply to this message link just above your post to view the message. Don't forget to sign in to Microsoft Community Forum to view the link.
I'll look forward to your reply.
Thank you.