Hi, I'm John! I will help you with this.
Can you please check if your Outlook (Attachments) storage is full?
If your mailbox is near or over the storage limit, new emails might not arrive in your inbox https://onedrive.live.com/managestorage in the same page, please check your OneDrive storage as it's linked to your Microsoft account and can sometimes affect email services if it's full.
To be safe, I recommend the following steps:
Check your account rules and forwarding settings, hackers create rules that automatically forward or delete emails. You can do this in Outlook settings under Mail > Rules and Forwarding. https://support.microsoft.com/office/manage-email-messages-by-using-rules-in-outlook-c24f5dea-9465-4df4-ad17-a50704d66c59
Just to be safe, I’d recommend to sign out everywhere. Visit: https://account.live.com/proofs/manage/additional Scroll down to Sign me out and select "Sign me out".
And changing your password again and enabling two-step verification if you haven’t already. This will add an extra layer of security to prevent future unauthorized access.
Click "Add comment" to let me know.
Regards,
John J.D.