Resolved: Known Error impacting Yammer
Microsoft has restored inbox and feed functionality to the service. Their work to restore real-time notifications continues.
Preliminary root cause: A portion of the infrastructure that accepts and routes incoming connections to the service is degraded, which impacts access to the Yammer site as well as real-time notifications and viewing messages from an email inbox.
More information: Resolved: Known Error impacting Yammer
Story added 18. July 2017, content source with full text you can find at link above.