Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi Geoffrey,
Greetings...!!
Thanks for posting and I apologize for delayed response. Please check if your tenant allow users to join external networks. Please log-in to Office 365 portal and access Yammer. Please navigate to Network admin in Yammer and click on External networks. Please check if the external network directory is disabled. Please check if admin approval is required for users to join external networks.
I hope this helps your query. Please reply if you have any query or issue regarding Yammer and we will get back to you.
Thanks and Regards,
Manish
Microsoft Yammer Support