Remote server returned '554 5.7.0 < #5.7.520 smtp;550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)>'

Question

Hi Guys,

I tried sending attachments via my newly created email account and am getting this message. Ive read this can be fixed in the back end of my account. can you please urgently assist?

I can no longer send emails.

Thanks.

Answer 1

Well in that case since free Outlook has daily limits, you need to slow down a bit, or upgrade to a Microsoft 365 subscription. There is no other way :(

Answer 2

Alright, thanks.

Please fill https://sender.office.com as a next step and the block should be removed in the next 48 hours.

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

Otherwise, if your problem is resolved, please take a moment to rate the answer. Wishing you good luck!

Answer 3

Hi,

This is because Microsoft's built-in systems think you are sending spam emails since you mentioned attachments. The best way is to wait for a few days or ofcourse buy a Microsoft 365 subscription.

Do you have any signature in your Email? If so, could you please remove that temporarily and verify?

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

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.

I’m eager to hear back and work together to find a solution.

Answer 4

Hi Ive tried all of the above and cannot send a single email saying test. Cna you please help.

Answer 5

The error 554 5.7.0 / 550 5.7.520 Message blocked because it contains content identified as spam. AS(4810) means Outlook.com/Hotmail is classifying the message content (or attachments) as spam and blocking delivery.

Because this is happening on a newly created Outlook.com account and affects all messages with attachments, the cause is most likely server-side spam filtering or a backend issue on the account. This cannot be fully corrected from the Outlook Web or client settings.

Actionable steps:

1. Test without attachments
   • Send a plain-text message with no links or attachments to a known, trusted address.
   • If that sends successfully, the filter is specifically reacting to the attachment content or type.
2. Simplify the attachment/content
   • Try sending a single, small, common file type (for example, a simple .pdf or .docx) with a short, neutral subject and body (for example, “Test document”).
   • Avoid:
     • Compressed archives (.zip, .rar) in the initial tests.
     • Many links or marketing-style wording in the body.
3. If all attachment attempts still fail
   • This points to a backend/account-level issue rather than client configuration.
   • In similar Outlook.com/consumer scenarios, issues with sending (especially for new accounts or spam-related blocks) have required Microsoft support intervention or were acknowledged as known bugs that were fixed on the service side.
4. Contact Microsoft support for Outlook.com
   • Use the in-product support path (for example, from Outlook on the web: Help → Contact support) so the support team can:
     • Check whether the account has been temporarily restricted by automated anti-spam systems.
     • Review server-side spam policies and logs for the specific error AS(4810).
     • Apply any necessary backend fixes or remove an incorrect spam block.
   • Clearly state:
     • The exact error: 550 5.7.520 Message blocked because it contains content identified as spam. AS(4810).
     • That the account is newly created and that sending without attachments works (if confirmed), but any message with attachments is blocked.
5. Continue to use the account normally
   • While waiting for support, avoid repeated rapid sending of similar blocked messages, as that can reinforce automated spam suspicion.

If the problem is a known backend bug or an incorrect spam flag on the account, only Microsoft support can clear or adjust it; there is no Outlook Web setting that will bypass this specific 5.7.520 spam block.

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References:

• Outgoing emails with attachments undelivered as spam - Microsoft Q&A