message blocked (554 5.7.0 )

554 5.7.520 ... Message blocked because it contains content identified as spam. AS(4810) means the message was flagged as spam by the mail filter.

For an Outlook.com/Hotmail account, the supported self-service checks are:

1. Send a simple test message from Outlook on the web.
   • Remove attachments, links, signatures, repeated text, and HTML formatting.
   • Send plain text only to a single recipient or to the account itself.
   • If that works, add content back step by step to identify what triggers the block.
2. Reduce recipient count.
   • If the message is going to a group, try sending to one recipient first.
   • Large recipient groups can make troubleshooting harder and can contribute to spam filtering outcomes.
3. Switch message format to Plain text in Outlook.com.
   • Open Settings > Mail > Compose and reply.
   • Change the message format to Plain text.
   • Test again.
4. Verify the account if prompted.
   • Newly set up or verification-pending Outlook.com accounts must complete the verification email step before they can send messages.
5. Review Outlook.com junk and sender settings.
   • In Outlook.com, go to Settings > Mail > Junk email.
   • Check for unusual blocked senders or rules.

If messages are still blocked after testing with a plain-text message, no attachments, no links, and a single recipient, use the Outlook.com support path in Help or the Outlook.com support/contact options listed in the delivery-failure article.

References:

• Sent email in Outlook.com comes back "delivery failed" | Microsoft Support
• I am just setting up an Outlook.com account and I'm unable to send email. | Microsoft Support
• emails undeliverable - Microsoft Q&A Remote server returned '554 5.7.0 < #5.7.520 smtp;550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)>'
• Remote server returned '554 5.7.0 < #5.7.520 smtp;550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)>' - Microsoft Q&A I have tried many times to send my group email and it is coming back as undeliverable.
• I can’t send emails. All are marked as spam - Microsoft Q&A