Thank you for reaching out to Microsoft Q&A forum.
To help narrow this down, could you please confirm:
- Are you accessing this Hotmail account via Outlook.com (web) or the Outlook app (Windows / Mac / mobile)?
- When you sign in directly at https://outlook.live.com, do you see your emails in the Sent Items folder there?
This will help determine whether the behavior is related to the account itself or only to a specific app/device.
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