Dear Jessi Ljungberg1,
Thanks for using Microsoft products and posting in the community.
I understand that you received an email from yourself which is usually a common phishing scam or threatening email.
It's great that you have a great sense of security. But this situation is indeed unsettling, now you can refer to the following information about how it was sent from your address:
You can view internet message headers: View internet message headers in Outlook - Microsoft Support to check if the email address shown is different from the sender's real address. You can also try sliding down to find the information of [X-SID-PRA], and the address behind this information is the actual sending address. Then you can add it to your blocked senders list.
If you encounter any problems during this process or if the problem persists, such as if the X-SID-PRA field is encoded in UTF-8, please let me know, you can provide me with screenshots of the problem and detailed information, I am more than happy to continue to help you.
For more information on identifying and handling fraudulent emails, please refer to the following link: Phishing and suspicious behavior in Outlook - Microsoft Support
You can learn more about account security and take measures to protect your account here: How to help keep your Microsoft account safe and secure - Microsoft Support
Hope this help you, please feel free to let me know how it goes. If there is any deviation in my understanding, please forgive me and provide me with more details. I am more than happy to continue to help you.
Best Regards,
Addie.C - MSFT | Microsoft Community Support Specialist