Message from Microsoft at https://portal.office.com/servicestatus
Title: Yammer sign in issue
User Impact: Users may be unable to sign in to Yammer.
More info: During the maintenance work, if users can sign in successfully they may see additional features in a degraded state. For example, message posting and notifications may not function.
Current status: As the maintenance work is ongoing, we're continuing our efforts to mitigate the issue. We're moving users to alternate healthy infrastructure.
Start time: Thursday, January 4, 2018, at 3:20 AM UTC
Next update by: Thursday, January 4, 2018, at 12:00 PM UTC