Enable @mentions for Office365 guests in Word, Excel, and other applications
The existing @mention only works for internal users within a tenant. For organizations collaboratively partnering with other organizations on an ongoing basis (e.g. marketing agencies, law firms, etc.), this is a critical component of alerting collaborators and highlighting relevant document changes. Even if just an email address could be tagged, that would be enough to get users in my tenant to quick telling me they want to go back to Google Suite.