Message identified as SPAM "Remote server returned '550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)'"

Hi @Fotini Pratis

Thank you for reaching out, and I’m sorry to hear you’re having trouble sending emails. I understand how inconvenient this can be, especially when important messages aren’t going through as expected. 

Based on the error message you received, it’s possible that the emails are being flagged as spam by the recipient’s mail server, often part of Microsoft’s Outlook or Microsoft 365 system. This may be related to how the message content is interpreted by their spam filters, rather than a technical issue or the type of attachment used. 

Here are some steps to help resolve this: 

Review your email content

Review your email for common spam triggers. Avoid using excessive promotional language, overly complex formatting, too many links, or too many images. Keep your messages clean and direct. 

Check your domain’s email authentication

If you manage your own domain, ensure your SPF, DKIM, and DMARC records are correctly configured. These are crucial for verifying your email's legitimacy and significantly reduce the chance of it being blocked by spam filters.

If you're sending emails from your own server or domain, your IP address may have been blacklisted by Microsoft’s filters. You can request removal through the official portal: https://sender.office.com. 

The article “Fix error code 550 5.7.1 in Exchange Online” provides helpful context for issues similar to yours. While your specific error is 550 5.7.520, the guidance may still offer useful best practices. You can view it here: Fix error code 550 5.7.1 

If the issue continues after trying the above steps, we strongly recommend contacting Microsoft Support directly. They can investigate specific blocks related to their anti-spam systems. 

• For personal accounts: click the Help (?) icon at the top right, and select Contact Support. 
• For Microsoft 365 business users: Please log into the Microsoft 365 Admin Center and go to Help & Support > New service request to submit the issue. 

We understand how inconvenient this is, and we’re here to support you every step of the way. If you’d like, we can help review your email content or provide further guidance on how to avoid future delivery issues. 

Please don’t hesitate to reach out if you need any assistance. 

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