Stop "Discover what's happening across your organization" emails from Yammer

Office 365 - How to stop "Discover what's happening across your organization" emails from Yammer being sent to All Users with an Exchange Online Transport Rule 

Yammer "Discover what's happening across your organization" email notifications

By default all users will get daily email digests and updates from Yammer

Individual users can change their notification settings but there is no global setting for admins to turn off emails from Yammer for all users

Remove Yammer license

You can remove the Yammer license using the Office 365 admin portal

Users - Active Users - select user account
Licenses and apps
Yammer Enterprise: Off

Exchange Online Transport Rule to redirect Yammer emails

To workaround the fact that we can't manage Yammer email digests for All Users. We will use an Exchange online transport rule to direct Yammer emails to an admin mailbox.

Yammer emails can come from these addresses:
notifications@yammer.com
noreply@yammer.com
notifications@eu.yammer.com

Create Exchange Online transport rule

Exchange admin center

Mail flow - Rules
Add a rule - Create a new rule

Rule conditions

Name
Forward Yammer emails

Apply this rule if
The sender address includes any of these words yammer.com

Do the following
Redirect the message to these recipients itadmin@yourdomain.com

Rule settings

Rule mode: Enforce

Click Finish 

Enable the rule

Reference:

Configure email and Yammer
https://learn.microsoft.com/en-us/yammer/configure-your-yammer-network/configure-email-and-yammer

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