Entra ID Multi-Tenant Organizations
Av Emil Björk · Microsoft-ekosystemskonsult, Göteborg
MTO is Microsoft's modern model for running multiple Microsoft 365 tenants as one organisation. Here's what it provides.
Organisations end up with multiple Microsoft 365 tenants for many reasons — acquisitions, regulatory separation, subsidiary autonomy. Historically, running multiple tenants meant lots of cross-tenant friction. Microsoft Entra ID Multi-Tenant Organizations (MTO) is the modern feature designed to make that less painful.
What MTO provides
When two or more tenants are joined as an MTO:
- Cross-tenant user synchronisation: users from one tenant are auto-provisioned as B2B guests in the other tenants, with attribute sync.
- Cross-tenant access policies are streamlined — the trust between MTO members is configured once.
- Unified people search across MTO tenants, so users from one tenant appear in the address book of another.
- Shared channels in Teams work cleanly between MTO members.
- Cross-tenant search in Microsoft Search — find content across all member tenants.
- Microsoft 365 Copilot can ground answers across tenants the user is a member of.
The user experience is closer to "one big company" while preserving tenant-level boundaries.
What MTO doesn't do
MTO is not a merger of tenants:
- Each tenant keeps its own licences, billing, Conditional Access, retention policies, and admin roles.
- Email addresses, SharePoint sites, and mailboxes remain per tenant.
- It doesn't replace a true tenant-to-tenant migration if you want one logical Microsoft 365 instance.
When MTO is the right choice
- Holding companies running multiple subsidiaries with separate compliance requirements.
- Recent acquisitions where a full migration is months or years away.
- Regulated industries where some business units must stay separate but still need to collaborate.
- Joint ventures where two organisations need to share a working surface without sharing identity.
Configuration
MTO is configured via Entra admin center under External Identities → Multi-Tenant Organization:
- The "primary" tenant creates an MTO and invites others.
- Each tenant joins by accepting the invite.
- Cross-tenant access settings are configured for inbound/outbound trust.
- Cross-tenant synchronization jobs are set up to auto-provision users between tenants.
Each tenant can leave the MTO at any time.
Limits
MTO supports up to a few hundred tenants in a single MTO as of 2026, with practical recommendations to keep it smaller. It's designed for organisations that operate as a federation, not as a public marketplace.
When to migrate instead
If two tenants are essentially one organisation that happens to have two tenants for historical reasons, a tenant-to-tenant migration is usually a better long-term answer than MTO. Tools from Microsoft (Mover, the M365 Migration Manager) and partners (Quest, BitTitan, AvePoint) automate the move. MTO is right when the separation needs to stay.