My outlook messages are being rejected by the receiver if I have an attachment on it.

Question

My outlook messages are being rejected by the receiver if I have an attachment on it.

Anonymous

Delivery has failed to these recipients or groups:

YuQi Patterson (******@hotmail.com)
Your message wasn't delivered because the recipient's email provider rejected it.

Diagnostic information for administrators:

Generating server: SJ2PR11MB8471.namprd11.prod.outlook.com

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

Original message headers:

Received: from SN7PR11MB8112.namprd11.prod.outlook.com (2603:10b6:806:2ea::18)
 by SJ2PR11MB8471.namprd11.prod.outlook.com (2603:10b6:a03:578::5) with
 Microsoft SMTP Server (version=TLS1_2,
 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8880.30; Tue, 1 Jul
 2025 16:59:58 +0000
Received: from SN7PR11MB8112.namprd11.prod.outlook.com
 ([fe80::5f50:25c5:63c:a336]) by SN7PR11MB8112.namprd11.prod.outlook.com
 ([fe80::5f50:25c5:63c:a336%4]) with mapi id 15.20.8857.026; Tue, 1 Jul 2025
 16:59:57 +0000
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
From: Art Patterson

Locked Question. This question was migrated from the Microsoft Support Community. You can vote on whether it's helpful, but you can't add comments or replies or follow the question.

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Answer accepted by question author

EmilyS726 270.7K Independent Advisor

Hello,

Any chance you are trying to send an email with a PDF attachment?

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 -

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

0 comments

1 additional answer

Answer 1

Anonymous

Thank you Emily,

I changed to plain text and it appears to have solved the problem.

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