Office 365 Groups and Teams support guest users, who enjoy full access to the SharePoint document libraries. You might not want this, because not every document in those libraries are suitable for sharing with guests. The question is how to collaborate with guests while maintaining some control over information. Rights management seems like a good way to accomplish the task.
Office 365 has given its rights management capabilities a complete refresh. Clients deal with protected email better and it’s easy to send protected email to people inside and outside your organization, including coverage of consumer email systems like Gmail and Outlook.com. And protected email works on mobile devices too.