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

Question

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

Nele Bieber 0

Dear Support Team,

I am experiencing a delivery issue when sending emails from my Outlook account. My messages are being blocked by the generating server (DS3PR22MB289160.namprd22.prod.outlook.com).

The remote server returned the following error message: 554 5.7.0 < #5.7.520 smtp;550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)>

Issue Details:

**my email address: ****@outlook.de
Recipient: ******@web.de
Error Code: 550 5.7.520 (Message blocked due to spam filter triggers)

The email I attempted to send was legitimate and did not contain spam. It appears that the automated spam filters have mistakenly flagged my message or my account's outbound reputation.

Could you please review this block, whitelist my email address if necessary, or let me know if there are specific elements in my email causing this false positive?

Thank you for your assistance.

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2 answers

Your answer

Answer 1

Hi, due to a lot of spam abuse, Microsoft has placed certain restrictions and imposed a daily limit on emails, especially if the email was recently created.

Sending limits in Outlook.com

https://support.microsoft.com/outlook/sending-limits-in-outlook-com

Also,

Do you have a signature in your Email? If so, please remove it temporarily and verify.

Second, try switching the Email to Plain Text instead of HTML as a troubleshooting step.

The setting is below:

Open The Gear icon > Settings.

Go to Mail > Compose and Reply.

Change the message format to Plain text.

User's image

If nothing works, file the form at https://sender.office.com and the restrictions will be lifted.

A friendly reminder that this is a user-to-user forum where users help other users.

Experts or Advisors participating here cannot make changes to Microsoft services or access internal systems and can only provide technical guidance, irrespective of Microsoft's Policy decisions.

I hope this information helps. If you have any more questions, don't hesitate to reach out.

Wishing you good luck!

Answer 2

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:

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.
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.
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.
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.
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.