MC1134737 - Microsoft Teams: Private channels increased limits and transition to group compliance

Message Center ID: MC1134737

Summary

Microsoft is updating private channels in Teams to use a group mailbox instead of individual user mailboxes. The change increases capacity and aligns private channel data with team-level compliance controls. Admins and compliance managers must act before migration begins.

What is changing

• Mailbox model: Private channel data moves to a channel group mailbox.
• Limits: Up to 1,000 total channels per team and up to 5,000 members per private channel.
• Meetings: Meetings can be scheduled in private channels.
• Compliance scope: Retention, legal hold, DLP, and eDiscovery must be applied at the team group level to govern post-migration data.

Who is affected

• Compliance managers: Purview retention, DLP, eDiscovery, and legal hold configuration.
• Tenant admins: Policy scope, migration monitoring, PowerShell checks.
• eDiscovery teams: Include both user mailboxes and group mailbox for complete results.
• End users: Possible duplicate search links during migration; functionality otherwise continues.

Why this matters for admins

• Post-migration private channel messages are governed by the team group policy, not user mailbox policies.
• Message edits and deleted messages are not copied to the group mailbox. Preserved copies remain in user mailbox holds until hold expiry.
• Existing private-channel-specific retention policies remain but cannot be edited. New private channel policies must be applied at the group level.

Action checklist (practical)

1. By September 20, 2025, apply existing legal holds, DLP, and retention policies to the team’s group where needed.
2. For eDiscovery, plan queries to include both user mailboxes and the team group mailbox to capture pre and post migration content.
3. Review team-level policies for consistency with private channel requirements and create equivalents if needed.
4. Watch for the new PowerShell command to track tenant migration status and update runbooks accordingly.

I recommend scheduling a short audit of teams with private channels now. That will avoid gaps when migration starts late September 2025.