Managing personal Outlook.com account settings, security, and privacy
Hi,
Welcome to Microsoft community and thank you for bringing this issue to our attention.
The possible reason of this issue is that you are a victim of email spoofing.
Email spoofing is the creation of email messages with a forged sender address - something which is simple to do because the core protocols do no authentication. Spam and phishing emails typically use such spoofing to mislead the recipient about the origin of the message.
We need to investigate the possible reason if you are victim of email spoofing we need some information from your sent message. Due to sensitivity of information we created a private message.
Please make sure you are signed in to view the private message.
Thank you