Unintended email delivery

Question

Hi, we have an issue where when someone sends an email to an address, some other users receive a copy of the email. For example, if someone with [Moderator note: personal info removed] sends an email to [Moderator note: personal info removed] receives the email as well.

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Moved from Microsoft 365 and Office | Other

Answer 1

As this forum is a public platform, we’ve taken steps to help protect your privacy by removing your organization’s domain name from your message. To ensure your data remains secure, we kindly recommend avoiding the inclusion of personal or organizational details such as domain names or screenshots with sensitive information in future posts.  

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Hi @BK, 

Thank you for reaching out to the Microsoft Q&A forum and for clearly outlining your concern. 

Based on the details you shared that when a user in your domain sends an email to an external recipient, an unintended copy reaches another internal mailbox. I appreciate the clear example and the time you have taken to test this from Outlook on the web. 

This behavior most often occurs when a mail flow rule in Exchange Online adds a blind copy or redirect on outbound messages. It can also result from mailbox level forwarding or an Outlook rule that runs on the sender’s account. In some cases an external address exists as a contact or shared object that a rule references, which consequently introduces the internal recipient. 

Below are some alternative steps designed to address your situation effectively: 

1/ Identify how the extra recipient was added using a message trace 

• In Outlook on the web open the sent item that produced the extra delivery and copy the Message ID from the message properties. 
• In the Exchange admin center sign in with an admin account, go to Mail flow, then Message trace, and run a trace for the sender within the relevant time window or paste the Message ID. 
• Open the trace result and review the event details for any listed rule name or action that added user email. Note any rule shown. 

2/ Review and adjust organization mail flow rules 

• In the Exchange admin center open Mail flow, then Rules, and locate any rule that targets messages from internal senders to external recipients or to the specific external domain. 
• If a rule adds a recipient, redirects, or blind copies messages, either disable the rule temporarily, narrow its conditions, or remove the action that adds user2 email. 
• Confirm the rule order so that only the intended rules apply, and consider enabling stop processing more rules where appropriate. Send a test message to verify the change. 

3/ Check forwarding and mailbox rules for the sender 

• In Outlook on the web for user email open Settings, then Mail, then Forwarding, and confirm that forwarding is not enabled to user2 email. 
• Still in Outlook on the web open Mail, then Rules, and remove any rule that forwards, redirects, or sends copies when you send messages. 
• In the Exchange admin center open Recipients, then Mailboxes, select user, and review Mail flow settings, then Forwarding. Ensure forwarding is off or not set to user2. Save changes and test again. 

4/ Contact IT administrator:  

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