how do you fix a 550.5.7.520 code. message blocked identified as spam AS(4810)

Julia O 25 Reputation points
2025-06-24T06:25:22.67+00:00

Outlook updated on Sunday. Prior to this emails worked just fine. Emailing the same workplace as usual. PDF's are used as attachments as requested by recipient. Problem seems to have only occurred once outlook was updated. Tried sending without attachments and email worked fine. I was able to reply to an email with attachments.

Outlook | Windows | Classic Outlook for Windows | For business
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Jayden-P 26,210 Reputation points Microsoft External Staff Moderator
2025-06-24T07:40:46.47+00:00

Hi @Julia O

Thank you for posting your question in the Microsoft Q&A forum. 

Based on the information you have provided, looks like you cannot send emails with PDF attachments.

I am so sorry about the inconvenience you are facing. We have received some reports about this known issue.

To resolve the root cause of this issue, you need to contact MS support team, they will collect logs and data and troubleshoot from the backend.

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Meanwhile, you can try this work around in the picture below.

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Or in your case, you can convert PDF file to PNG. It will be sent normally.

Since this bug doesn't affect mobile device, you can draft an email on your computer, then send it with your phone. It will be delivered successfully.

Once again, I apologize for the inconvenience this might cause you. I totally understand how frustrating and time consuming this would be for you.

We will try our best to resolve this issue to enhance customers' experience.

Thank you for your understanding.

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  1. EmilyS_726 34,465 Reputation points Volunteer Moderator
    2025-06-27T16:54:07.65+00:00

    Hello,

    More and more email services providers have updated their spam filters due to rising zero-day phishing PDF campaigns. PDFs + HTML email are commonly used in phishing, so security systems scrutinize these more.

    You can consider these alternatives if you need to send PDF attachment -

    1. Share it via a OneDrive link instead for the recipient to download.
    2. Zip it into a .zip file and attach it.
    3. If your email format is rich text/html, convert it to plain text.

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