In some cases, Outlook will not show the sent items in the sent items folder or elsewhere, this can be a result of a misconfiguration with Outlook and can be easily corrected.
Problem:
User cannot see sent items in the sent items folder
Possible Causes
"Save Sent Item To" option may not be set correctly
Outlook cannot connect to the Outlook server
Solution
Click New Email → Options Tab on new window → Click "Save Sent Item To" and select "Use Default folder" if not set already
Check the connection to the Outlook web server
If the issue is still not resolved...
Escalate the ticket to the next resource for further review and provided the steps taken to try and triage.