Microsoft is moving towards a new optimized collaboration and administration for organizations operating multiple M365 tenants. New Teams client is supporting this feature. Nevertheless, there are (today in public preview) limitations to MTO, which might be removed over time. Self-service of multitenant organization functionality is limited to a maximum of five tenants and 100,000 internal users per tenant. To request a raise in these limits, submit a Microsoft Entra ID or Microsoft 365 admin center support request. Further to me, it is NOT a real multi-tenant organization, as we know from earlier days in AD, where we had "SubDomains", it is based on automated B2B identities, which are provisioned as B2B users automatically. This is the sync feature in MTO. Below the extract from Microsoft blog release: Using shared channels for seamless cross-tenant collaboration and communication In a recent blog , we shared how Microsoft Teams Connect enables seamless and secure collabora