Hello NT E,
Welcome to Microsoft Community.
I am a Microsoft user just like you, I hope you are doing well.
Sorry for this inconvenience. It would appear that you are not the only user who is experiencing this issue.
"Your message can't be sent because it was rejected by the recipient's email provider.
Remote server returned '550 5.7.520 Message blocked because it contains content identified as spam. AS (4810)"
Hopefully, there will be some updates. However, I will suggest you exercise some patience as we hope that Microsoft will resolve this issue as soon as possible.
See thread with similar inquiry:
https://answers.microsoft.com/thread/6d115a6b-3df7-4eb5-85af-3eeb05c6d5db
Please let me know if you need more assistance.
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Warm Regards