Outlook Rule CC Group Creates Duplicates

Copper Contributor

Hi all. I have a user who has stumbled across an unexpected behavior and I wanted to see if anyone else had seen it and had any information. Here's the scenario.


User created rules when sending email. When a specific word was in the subject, the message would be CCd to a Microsoft 365 Group. 


The rule works as expected when sending a new email. The issue occurs when someone replies to the message. If the user then responds back, the CC rule triggers again and for some reason, sends two copies of the same sent message to the group. This continues, increasing the number of duplicate messages as the thread continues. 


While I can see how this is happening, I would expect either Outlook or Exchange Online to see the duplicate email addresses in the CC and only send one message. When using a CC rule to send to another user, we don't see this behavior. 


I suspect I'll need to report this to Microsoft but was hoping someone out there had more info first. Thanks in advance for your input. 

1 Reply
Best open a support case and report this.