Hello J.C. Hall,
It looks like you can overcome this issue by doing the following from an Apple workstation using Mail.
1. Open Mail and choose the “Mail” menu in the upper left. Select Preferences.
2. Choose the “Accounts” Tab at the top, then select the account you wish to adjust in the list on the left
3. Select the “Mailbox Behaviours” tab on the right
4. Under “Sent Mailbox” use the drop down to select the folder called “Sent”. Be sure that it is a folder underneath the header indicating your server-side email account and NOT “On My Mac” (that is a local folder). If you do not see such a mailbox, you will need to create it by choosing the Mailbox menu, then selecting New Mailbox. For the Location field, you must select the correct account to create it under (not On My Mac), then set the name to “Sent”.
Step 4 is where you should indicate the outlook Sent items folder.