Dynamics 365 and Yammer have built in integration. To turn on this integration, in Dynamics 365, go to Settings->Administration and select Yammer Configuration:
You will see this message:
Clicking Authorize Microsoft Dynamics 365 Online to connect to Yammer displays the window below. Click Allow:
This will then display additional options. Yammer is now connected.
Clicking on Edit message rules takes you to:
Now, when you perform actions in Dynamics 365, you will see a new Yammer tab. For example, in an account record, after following the record, you will be able to post to Yammer from the record:
Users will now see this message on the Yammer side.
To remove the Dynamics 365 and Yammer integration, you can go to Yammer->My Applications and select Revoke Access: