Send & Receive Issues

How to Fix Outlook Emails Rejected as Spam (Error 550 5.7.520)

Maira Mehtab Oct 13, 2026 868 views

Question details

Outgoing emails are suddenly being rejected by recipient mail servers and returning spam-related error codes.

How to Fix Outlook Emails Rejected as Spam by Recipient Servers

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Sending emails to individuals, groups, and multiple Microsoft accounts.
Observed behavior: Messages fail to send and return a non-delivery report (NDR) with an error such as '550 5.7.520 Message blocked because it contains content identified as spam'.

Before you start

Locate the exact Non-Delivery Report (NDR) in your inbox, as you will need the specific error code and rejection details for troubleshooting.

Solution 1Recommended

Review Microsoft Service Advisories and Contact Support

Since this error often stems from server-side spam filter updates or glitches, checking for Microsoft incidents and escalating the issue is the most effective approach.

Occasionally, Microsoft Exchange or Outlook servers experience widespread issues that cause legitimate emails to be falsely flagged as spam (AS: 4810). In these cases, the issue must be resolved by Microsoft.

Check Service Health

Log in to the Microsoft 365 admin center and navigate to the Service Health dashboard to check for any ongoing Exchange Online advisories.

Gather NDR Details

Open the rejected email bounce-back message and copy the exact error code (e.g., 550 5.7.520), the affected sender account, and the timestamp.

Check Community Updates

Visit the Microsoft Community forums to see if other users are reporting identical sudden rejection issues, which indicates a widespread server problem.

Contact Microsoft Support

Reach out to Microsoft Support via your admin portal or the help menu, providing the complete rejection message and details of the affected accounts.

Review Microsoft Service Advisories and Contact Support

Wait for Resolution: If multiple users are experiencing this simultaneously, Microsoft is likely already working on a patch. Keep an eye on official support threads for updates.

Solution 2

Modify Email Content and Sending Patterns

Adjusting your email habits and content can help bypass strict automated spam filters on the recipient's server.

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Frequently Asked Questions

What does Outlook error code 550 5.7.520 mean?

This error code indicates that the recipient's email provider or server has blocked your message because it was identified as spam by their automated filtering system.

Can I fix the spam rejection error on my own?

If the issue is caused by a widespread Microsoft server glitch, you must wait for Microsoft to resolve it. However, you can try removing suspicious links and sending plain text emails to see if specific content is triggering the block.

Why are emails to my own group members being rejected?

Strict spam filters can sometimes falsely flag bulk messages, board member updates, or group emails as spam, especially if they contain multiple links, attachments, or if the sending server reputation has temporarily dropped.

Where can I report this Outlook rejection issue?

You can report the issue directly to Microsoft Support through your Microsoft 365 admin portal, or post your issue on the official Microsoft Community forums along with the non-delivery report (NDR) details.

Outlook & Email Problems