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

Microsoft Teams is migrating private channels to use group mailboxes, increasing limits to 1000 channels per team and 5000 members per channel, and enabling meetings in private channels. Migration runs from October 2025 to April 2026. Admins must remediate ownerless channels by July 2026 or risk deletion. Compliance policies must be updated to apply at the team group level.