Teams Private Channels Migration Stalls: Admin Action Required by June 5, 2026

Microsoft updated Message Center notification MC1134737 on April 30, 2026.  The implications for legal hold, retention, and eDiscovery are immediate.

What Microsoft Announced

A quiet update to a Microsoft migration notice has given legal, compliance, and IT teams until June 5, 2026, to confirm that their legal hold, retention, and eDiscovery scopes still cover Teams private channel content, which has moved to a new storage location that many tenants have not yet finished adopting.  Microsoft updated Message Center notification MC1134737 on April 30, 2026, disclosing that what was announced in 2025 as a hands-off, automatic migration is, in many tenants, neither finished nor hands-off, and that affected private channels will be deleted unless administrators intervene by the June 5 deadline. 

In 2025, Microsoft announced a fundamental change to how Microsoft Teams private channel data is stored.  Under the old model, every member of a private channel kept their own copy of the channel’s messages inside that user’s personal mailbox.  Under the new model, a single copy of the messages is held in a new Private Channel Exchange Online Group mailbox.  However, if  a user mailbox is on hold, a copy of the historical private channel messages will remain in that mailbox until the hold is released.  Alongside the storage change, Microsoft is raising private channel scale limits (up to 1,000 channels per Team and 5,000 members per channel) and is adding the ability to schedule meetings inside private channels for the first time.  Microsoft said the migration would begin in late September 2025 and be completed by December 2025, with data moving automatically for every tenant in the background.  No admin action was required to start it.

What You Must Do Now

• Check your tenant’s migration status.  Microsoft provides a PowerShell command (Get-TenantPrivateChannelMigrationStatus) that reports whether your migration is complete, stalled, or requires admin attention.  Without running it, there is no visible warning in Teams or in the Purview portal related to the status of migration efforts.  [Tony Redmond offers a script to assist with the identification of private channel membership, including archived private channels here.]
• Fix ownerless or guest-only private channels.  Any private channel without an in-tenant owner must have one added by June 5, 2026.  Channels that do not have an owner assigned by that date will be soft-deleted (recoverable for 30 days, then permanently removed).  Existing retention policies and legal holds will still be honored, but operational access to the channel will be lost.
• Identify Archived Teams with Private Channels.  Private channels that belong to archived Teams will not be migrated through Microsoft’s automated process.  Those channels require the team to be unarchived first, and an in-tenant channel owner added, before the migration will progress.
• Re-scope Purview policies and extend legal holds to private channel mailboxes.  Private channel message content now resides in a private channel group mailbox rather than in individual users’ Exchange Online mailboxes, similar to how parent Team messages reside in the Team’s Exchange Online mailbox.  As a result, eDiscovery legal hold scope must include the Team group mailbox, the new private channel mailbox(es), the Team SharePoint site, and any private or shared channel SharePoint site(s).  For any Team already on legal hold that contains private channels, the private channel Exchange Online mailbox must be added to that hold as well.  Because Microsoft’s migration process will not remove pre-migration private channel messages from user mailboxes that are already on hold, any user mailboxes previously placed on hold to preserve private channel data should remain on hold until the existing hold expires.  
• Replace private-channel-specific retention policies.  Historical private channel retention policies are now read-only and can no longer be created or edited.  Companies should ensure the Teams channel messages retention policy in Purview Data Lifecycle Management is configured to the desired setting.  Going forward, this setting will cover standard, shared, and private channel messages together.

Why This Matters

The change is about where private channel content is stored.  Before the migration, every member of a private channel kept a copy of the channel’s messages inside that user’s own mailbox.  After the migration, a single copy is held in the private channel’s group mailbox.  That shift impacts anywhere legal, governance, or compliance depends on knowing where the data sits.  Going forward:

• For eDiscovery on a Microsoft Team, you must search both the individual user mailboxes (for pre-migration private channel history for users who were on hold or subject to a private channel retention policy prior to the change), the Team mailbox (for current standard and shared channel message data), the new private channel mailbox(es), and the SharePoint sites associated with the team and any private channels (each private channel has its own SharePoint site).
• For legal hold on Teams messages, the scope must now also include the private channel group mailbox(es).  Holding only the user mailboxes or the Teams group mailbox will not preserve new private channel message content.
• For retention, a single policy attached to the Team governs standard, shared, and private channel messages together.

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The views expressed in this article are those of the authors and do not necessarily represent the views of their law firm or any of its clients.