Teams private channel messages are moving to group mailboxes, and compliance managers must act before September 20, 2025, to avoid data loss and compliance gaps.
Microsoft is reengineering private channels to improve scalability and simplify governance. This change impacts Microsoft Purview eDiscovery, retention, and DLP policies.
This update was announced in the Microsoft Teams Blog and flagged in the Microsoft 365 Message Center (MC1134737).
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Why Teams Private Channel Compliance Matters
Before migration:
- Private channel messages stored in individual user mailboxes
After migration (Sept 20 onward):
- Private channel messages stored in the team’s group mailbox
Why this matters for compliance:
Policies scoped only to user mailboxes will no longer apply to new private channel messages after migration.
For full technical details, see the official Microsoft Teams announcement.
Migration of historical data
⚠️ The latest version of private channel message data from each user’s mailbox is moved to the group mailbox. For users under a retention or eDiscovery or Legal hold the Message edits and deleted messages will not be copied to the group mailbox but remain in preserved library folder of the user mailboxes until the hold expires.
Why Microsoft is making this change:
- Increase scalability (up to 1000 private channels per team, 5000 members each)
- Align compliance with shared channels
- Enable new features like scheduling meetings in private channels
Compliance Risks if You Do Nothing
| Area | Before Migration | After Migration | Risk |
| eDiscovery & Legal Hold | Messages in user mailboxes | Messages in group mailbox | Holds/searches scoped only to users will miss new content |
| DLP | DLP scoped to user mailboxes | DLP scoped to group mailbox | Sensitive data in private channels could bypass detection |
| Retention | Retention applied to user mailboxes | Retention must apply to group mailbox | New content may not meet regulatory retention requirements |
Example: During a regulatory investigation, if your legal team searches only user mailboxes, post-migration private channel data will be excluded, weakening evidence collection.
Key Actions for policies and holds scoped to Teams Private Channel Messages
✅ 1. eDiscovery & Legal Hold
- Before migration:
- If a legal hold exists for a private channel, apply it to the team’s group mailbox in addition to user mailboxes.
- After migration:
- For complete eDiscovery, include both user mailboxes (pre-migration) and group mailboxes (post-migration).
- Note: For users under hold the Message edits and deleted messages will not be copied to the group mailbox but remain in user mailboxes until the hold expires.
“If you had Sally’s mailbox on hold because of private channels, that data will move to the group mailbox. If the team isn’t on hold, you risk data loss.” – Nikki Chapple
✅ 2. Retention Policies
- Before migration:
- Apply retention to the team’s group mailbox for Teams channel messages.
- After migration:
- You cannot create new private channel-specific policies.
- Existing private channel policies become read-only but can be deleted.
- Policies applied to the team’s group apply to all channels in the team.
“If retention policies aren’t aligned, data could be deleted irrecoverably once migration starts.” – Nikki Chapple
✅ 3. DLP Policies
- Before migration:
- Modify “Teams chat and channel messages” policies to include the team’s group in addition to user mailboxes.
- After migration:
- Ensure DLP policies are scoped to the team’s group mailbox.
“If you’re using automation or third-party tools for holds and communications, make sure they’re updated to reflect the new data location. Otherwise, your DLP and compliance workflows could break.” – Ryan John Murphy
Action Checklist: What You Must Do Before Sept 20, 2025
✔ Monitor Message Center (MC1134737) for updates
✔ Update eDiscovery holds to include group mailboxes
✔ Review and align retention policies
✔ Update DLP policies for Teams
✔ Validate migration using Microsoft’s upcoming PowerShell command
✔ Document all changes for audit readiness
Other Enhancements to Private Channels
- Up to 1000 private channels per team (previously 30)
- 5000 members per private channel (up from 250)
- Schedule meetings in private channels
- Unified compliance management via team’s group mailbox
Timeline
- Migration starts: Late September 2025
- Migration completes: By mid-December 2025 (tenant rollout timing may vary)
FAQs
How can admins identify a user’s private channel memberships?
Use Teams Admin Center or PowerShell: Get-TeamChannelUser.
Why isn’t Microsoft automatically applying policies from user mailboxes to the group?
It is up to organizations to decide the right scope for their policies and holds.
What happens to existing retention policies for private channels?
They become read-only. You can delete them but not edit them.
Do I need to update my eDiscovery cases?
Yes review all open cases. Add group mailboxes for any teams with private channels under investigation. For users under hold the Message edits and deleted messages will not be copied to the group mailbox but remain in user mailboxes until the hold expires. So keep the existing holds on the user mailbox.
Will old private channel data move automatically?
Yes, but message edits and deleted messages remain in user mailboxes.
Will I be able to track the progress of the migration?
Microsoft will be releasing a PowerShell command to check whether their migration has started or is completed.
More information
Watch or Listen to the full episode
📺 YouTube 👉 All Things M365 Compliance – Teams Private Channel Changes
Read the announcement on the Teams Private Channel changes here Microsoft Teams Blog
As an admin, follow the Microsoft 365 Message Center change, number MC1134737.
📖 Want to know more about what data is stored where? Read my blog on Ultimate Guide: Microsoft 365 Data Storage Locations
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