Additional chat-related features and issues within Microsoft Teams for business
With the current setup (separate tenants with guest access), a single unified chat list across both organizations in one Teams view isn’t available. Each tenant still has its own chat context, so chats appear only when switched into that tenant/org.
There are two relevant options from the provided information:
- Guest access / external access (your current model)
- Users can be members in their home tenant and guests in the other tenant.
- A Teams user can only use Teams in one tenant at a time; to collaborate with people in the other tenant, that user must switch tenants.
- This is explicitly called out as a limitation: a user “can only collaborate with technicians in Tenant Contoso1 if [they are] using Teams in Tenant Contoso1… To switch tenants in Teams desktop, select your profile picture, then select the tenant you'd like to switch to.”
- Multitenant organization (MTO) in Microsoft 365
- If the two tenants are under the same organizational control, they can be configured as a multitenant organization.
- In an MTO, users are synchronized between tenants using Microsoft Entra B2B collaboration users.
- With the new Microsoft Teams desktop client, users can:
- Search for users in other tenants in the multitenant organization.
- Receive real-time notifications from all tenants in the multitenant organization.
- Participate in chats, meetings, and calls across all tenants without needing to switch tenants.
- MTO-specific Teams functionality requires full MTO setup, including external access and B2B direct connect policies.
Given this, for a merger scenario where both tenants are under the same company’s control and will eventually be consolidated, the supported way to get closer to a “single view” experience (no constant tenant switching) is to:
- Plan and set up a multitenant organization between the two tenants.
- Ensure the new Teams desktop client is used, as it supports real-time notifications and cross-tenant collaboration in an MTO without tenant switching.
Until an MTO is configured, the behavior described—needing to switch orgs to see chats started from the other tenant—is expected and cannot be removed just by using guest access.
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