Hi,@mcdy
Thanks for posting your question in the Microsoft Q&A forum.
Based on your description, I'd like to confirm the issue with you.
After you set DelegateSentItemsStyle = 1, some users' emails are saved to both shared and “Sent Items” mailboxes?
If this is the problem, Microsoft has provided an official solution, please refer to this link:https://learn.microsoft.com/en-us/outlook/troubleshoot/email-management/email-remains-in-the-outbox-when-you-use-the-deleg?source=recommendations
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