Microsoft Teams, a part of Office 365, enables collaboration using people, conversations, content, and apps to enable successful team interaction. Previously guest members of the team must have an Azure Active Directory account. This is now no longer required. Although a Microsoft account is required, the individual can have an email account from domains such as gmail, yahoo, or any corporate email domain. If the individual within the team does not have a Microsoft account linked with that email address, Microsoft will simply assist them in obtaining this on the fly.
Teams provides the same enterprise-grade security as it does with other like products. Admins have the ability to monitor and report on the activities of these external guests.
One of the questions I have is how this relates to many of the channels or other integrations with Teams. For example, Stream has always been an AAD account only product. Is this now expanding its guest account capabilities? Microsoft has posted back that the two are not related and Stream content will still only be accessible to AAD team member accounts.