Delivery Failure: Outbound email blocked as spam (Error 550 5.7.520)

550 5.7.520 means the message was blocked by spam filtering because the content was identified as spam.

For an Outlook.com account, the supported actions are:

1. Send a simple plain-text test message with no attachments and no links.
   • If that works, the block is likely triggered by message content or formatting.
2. Review the message for common spam triggers.
   • Remove large attachments.
   • Remove shortened or suspicious-looking links.
   • Avoid repeated text, heavy HTML formatting, or overly promotional wording.
3. If an attachment is required, try an alternative.
   • PDF attachments can be scrutinized more heavily by spam filters.
   • A OneDrive link can be used instead of attaching the file.
   • Converting the message to plain text can also help.
4. Check the Outlook.com account for anything unusual.
   • Verify account security at https://account.microsoft.com.
   • In Outlook on the web, review Settings > Mail > Junk email and check for unusual blocked senders or rules.
5. If messages start failing from multiple devices or continue after simplifying the message, use Outlook.com Sender Support.

The request to whitelist the address or manually review the block is not a self-service action in the provided guidance. The practical next step is to reduce spam-like content in the message and, if the issue persists, contact Outlook.com support through the product support path.

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