Short version:
With this update, admins of Yammer networks aligned to native mode can enable external collaboration so that Yammer community admins may invite guests to a community. Off by default. Public preview > general availability late March.

Details:
If you are an end user, you may have to speak to your Yammer admin to have this enabled.

With this update, admins of Yammer networks aligned to native mode can enable external collaboration so that Yammer community admins may invite guests to a community.

By default, guest access is turned off.

  • You can enable and disable guest access on a per community basis.
  • You can control which users can invite guests into the tenant.
  • You can easily configure email domains to allow and disallow guests.
  • Rich audit logs allow you to review all guest actions in your tenant.

To allow guest access, go to Yammer network admin center > Security Settings > External messaging settings.

  • After you enable guest access, community admins can invite guests to the communities to facilitate rich collaboration inside the community.
  • You can also turn off guest access at any time. Turning off guest access prevents community admins from being able to add new guests.

Availability:
The feature moves from public preview to general availability in late March.

Links:
Related blog: Guest Access in Yammer using Azure AD B2B is now in preview!