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Ho to fix Remote server returned '550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)'

Jasmine Beddows 0 Reputation points
2025-07-12T22:31:49.8133333+00:00

When I try to send emails with pdf attachments the email doesn't get sent and the returned email has the following:

Your message wasn't delivered because the recipient's email provider rejected it.

Remote server returned '550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)'

Outlook | Windows | Classic Outlook for Windows | For business
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  1. EmilyS_726 760 Reputation points Volunteer Moderator
    2025-07-13T01:36:39.8566667+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. Probably quickest and easiest, if your email format is rich text/html, convert the email (not the PDF) to plain text.

    Instruction can be found here: https://support.microsoft.com/office/change-the-message-format-to-html-rich-text-format-or-plain-text-in-outlook-338a389d-11da-47fe-b693-cf41f792fefa
    Screenshot 2025-07-08 103720

    1. Share it via a OneDrive link instead for the recipient to download.
    2. Zip it into a .zip file and attach it.
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