Message blocked because it contains content identified as spam (AS(4810))

Question

I manage email communications for a community brass band using the Outlook.com address ******@hotmail.com. We have 53 members in our contact list, and we send regular updates about rehearsals, events, and participation requirements. These are legitimate, non‑commercial group messages sent only to our band members.

Recently, our outgoing messages have been blocked with error 550 5.7.520 – Message blocked because it contains content identified as spam (AS(4810)). This appears to be an automated bulk‑mail restriction, but our messages are not spam and the account has not been compromised.

Could you please review and remove this sending restriction, and whitelist our account so we can continue sending legitimate group communications to our members? The ability to email our full contact list is essential for coordinating band activities.

Thank you for your assistance.

Greg Morris

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.

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

The setting is below:

1. Open The Gear icon > Settings.
2. Go to Mail > Compose and Reply.
3. Change the message format to Plain text.

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

https://yourwindowsguide.com/2026/09/550-5-7-520-message-blocked-error.html

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!

A Windows MVP writes content on the above website, so it is safe. However, do watch out for the ads. It should translate into your Browser language automatically.

Answer 2

A sending restriction or whitelist change cannot be performed here. For Outlook.com, the supported actions are:

1. Send a simple test message from Outlook.com with no attachments, links, or complex formatting.
2. If a signature is configured, remove it temporarily and try again. Signatures can affect sending.
3. Change the message format to plain text in Settings > Mail > Compose and Reply, then test again.
4. Review message content for common spam triggers such as excessive links, URL shorteners, embedded scripts, image-only content, or other formatting that can resemble spam.
5. If the account is new or recently triggered verification prompts, note that Outlook.com can apply a temporary low sending quota until account credibility is established.
6. If a non-delivery receipt is received after confirming the recipient addresses are correct, use Sender Support in Outlook.com.
7. If self-help does not resolve it, use Outlook.com support from Help in Outlook.com and select Contact Support.

For Microsoft 365 business tenants, admins can investigate with Exchange admin center > Mail flow > Message trace, but that does not apply to a personal Outlook.com mailbox.

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References:

• Can't send or receive email in Outlook.com
• I can’t send emails. All are marked as spam - Microsoft Q&A
• emails undeliverable - Microsoft Q&A
• Outgoing email not working - Microsoft Q&A
• Receiving email from blocked senders in Outlook.com