HERE you GO !. I have tried to enable/add guest access in my O365 trial tenent and share it below.
Login to your Microsoft Teams console and add guest. Remember that you can only add (Tenent O365 emabled)
Add guest by putting valid email address of O365 tenent.
Upps, you got error saying that “you are not authorized”??. OK, never mind.
go into Microsoft Teams settings in the Office 365 admin portal. From within the admin portal navigate to Settings -> Services & add-ins -> Microsoft Teams. On the fly-out to the right, under the section Settings by user/license type click the drop-down menu and toggle from Business and Enterprise to Guest then click On next to Turn Microsoft Teams on or off for all users of this type. Then click Save, and then try to add same member
YOu can also validate the guest was successfully added to Azure Active Directory
Browse to https://aad.portal.azure.com . On the left pane, click Azure Active Directory. On the Azure Active Directory blade clickUsers and groups
Guest user will be receiving email as email invite to join the channel from “Microsoft Teams <email@example.com>”
Guest user can login as guest on link and start conversation.
BUT – Honestly, Microsoft has to do lot of other improvement if really want to compete with Slack 🙂 🙂
Enjoy and happy Teaming !!!