How do you fix this message

Question

Getting this message when sending an email within office from one person to another person in the office. It is a word document. How do you fix it?

Error message:

 *550 5.0.350 One or more of the attachments in your email is of a file type that is NOT allowed by the recipient's organization.*

Answer 1

Hi @KimM, 

Thank you for reaching out to the Microsoft Q&A forum.  

Based on your description, you are receiving error 550 5.0.350 indicating that one or more attachments are not allowed when you send a Word document to a colleague inside your organization using classic Outlook. I recognize the impact on your day to day workflow and sincerely appreciate the details and effort you have shared. 

This typically occurs because the recipient organization enforces security policies that block certain attachment types or file characteristics, even for internal mail. Word files that include active content such as macros, are saved in the older .doc format, or are encrypted or password protected can trigger attachment protection. In some environments, mail flow rules or a third party email gateway may also apply additional restrictions that block delivery. 

Below are a few practical solutions that could best fit your current needs:  

1/ Validate the file format and content 

• Open the document in Word and save a fresh copy as .docx.  
• Remove any macros and confirm the file is not encrypted or password protected by going to File, Info, Protect Document and clearing any protection.  
• Rename the file to a simple name with a .docx extension and try sending it again. 

2/ Use a Microsoft 365 sharing approach 

• Upload the file to OneDrive or SharePoint and share a link with people in your organization. 
• In Outlook, you can choose Attach File and select the cloud location to send it as a link.  
• If your policies allow it, you may also compress the document into a zip file and attach that instead. 

3/ Isolate where the block occurs 

• Send a clean test .docx that contains only plain text to the same recipient.  
• Then send the same file to a different internal recipient.  
• Next, try sending from Outlook on the web. Note the exact time of each attempt and keep any non delivery report details.  
• This helps determine whether the block is tied to the file, the sender or recipient, or a broader policy. 

4/ Contact IT administrator 

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. 

• In the Exchange admin center, review Mail flow and Rules for any rule that blocks attachments by file type or by pattern.  
• In the Microsoft 365 Defender portal, check Threat policies including Anti malware and Safe Attachments to confirm whether macro enabled Word files or older formats are blocked for internal messages.  
• If required, create a targeted exception for internal sender to internal recipient for compliant .docx files, then allow time for policy propagation and test again. 
• If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.      
  • They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn   

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.    

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.      

Thank you for your patience and your understanding.

I look forward to continuing the conversation. 

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Answer 2

The error message 550 5.0.350 indicates that one or more of the attachments in your email is of a file type that is not allowed by the recipient's organization. To resolve this issue, you can try the following steps:

1. Check Attachment Type: Ensure that the Word document you are trying to send is in a file format that is permitted by the recipient's organization. Common acceptable formats include .docx and .doc.
2. Compress the File: If the document contains embedded objects or is too large, consider compressing it into a .zip file before sending.
3. Consult with IT: If you are unsure about the allowed file types, consult your IT department or the recipient's IT department for guidance on what file types are permitted.
4. Use Alternative Methods: If the attachment is still not allowed, consider using a file-sharing service to share the document instead of sending it as an email attachment.

By following these steps, you should be able to address the issue and successfully send your email with the attachment.

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References:

• Fix NDR error "550 5.0.350" in Exchange Online