When using Yammer it looks at the to email address in the envelope, not the members list. I have been asked a few times on how to include a Yammer group in a DL. For example, you send to a DL called “Support Questions”, and you want that to go to people and a Yammer group called Support Questions, well here is my solution for this. I hope that Microsoft would fix this so that you could simply create a contact and add it to a DL, but that does not work yet.
- Go to the group
- Go to Info and under access options there is a button for email to this group, and copy the shortcut used, for example: mailto:GroupNamefirstname.lastname@example.org
- By the group name there is a gear icon, there you can set the permissions. You would set the content to private or public. If you set it to private then anybody that can send to that group in Exchange must be able to send to that group in Yammer
- Create a new Hub transport Rule
- When Any of the recipients in the to or cc field is: the Distribution Group
- BCC the message to: the email address of the yammer group (Use BCC to prevent mail loops)