Private channels - no longer the black sheep of governance?

Discusses an update (MC1134737), which promises to simplify the way that retention is applied to private channels.

The current challenge of governing private channels

Private channels were first introduced into Microsoft Teams back in November 2019. I’m assuming that most of you are familiar with the way that they work, but for those who are not, they provide an area which can only be accessed by selected users in the Team. In my experience, users tend to find private channels really intuitive – an easy way to secure content, while still keeping it within the context Team.

Of course, under the hood, things are a little more complicated. Messages created in private channels are stored in individual user mailboxes (unlike standard channels, where they are stored in the group’s shared mailbox). Likewise, files are uploaded into a different SharePoint site for each private channel (unlike standard channels, which all use the Group’s primary SharePoint site for storage of files).

These underlying technical differences have made information governance in private channels rather challenging!

For example, at the time of writing, in order to undertake an eDiscovery search, each private channel needs to be individually included in your query, otherwise content contained within isn’t included in your results. This of course means that legal holds are only applied to content in private channels if those channels were explicitly included in your eDiscovery queries.

Another example can be seen when attempting to apply retention to private channel messages. With standard channels, a retention policy is associated with the Group – meaning that you could easily apply different retention to messages in different Groups (for example allowing you to delete messages in lower-value Groups on a timely basis, while ensuring that higher-value Groups (such as say an Executive Committee), are retained for longer).  However, private channels require a separate retention policy, which is pushed out to users and not to Groups. This means that your private channel messages are retained in accordance with who posted them, rather than the type of activity being undertaken.

What’s about to change?

On the 20^th of September 2025, Microsoft is deploying the following change (MC1134737):

“Microsoft Teams is enhancing private channels by increasing limits to 1000 channels per team and 5000 members per channel, enabling meetings, and shifting compliance policies from user mailboxes to team group mailboxes. Migration starts late September 2025; admins must update policies by September 20, 2025.”

The headline features of this change are:

• A significant increase in the maximum number of private channels in a Team

The maximum number of private channels allowed in a Team is increasing from 30 to 1,000. Don’t forget, each private channel has its own SharePoint site. So, that’s potentially more than one thousand  sites associated with a single Team!

I’m sure some will take advantage of this new limit, but my guess is that very few organisations will see any of their Teams exceed the previous limit of 30 private channels.

I feel that this increase makes it even more essential that you introduce processes to automatically configure every new private channel that is created (and ensure that these processes apply appropriate content types, metadata, sensitivity labels and retention labels). NB, for those of you interested, Orinoco 365 is the only tool I’m aware of that can do this for you!

• A significant increase in the number of users in a private channel

The maximum number of users in a private channel is increasing from 250 to 5,000.

While I’ve never come across anyone complaining about the previous 250 limitation, I’m sure this will be really useful for organisations close to this limit.

• Private channels will switch to use the Group’s shared mailbox

To me, this part of the update is the most significant for Information Managers. It means that the way we apply Purview’s compliance capabilities to private channels is changing (and mostly becoming simpler), however, there are ramifications for retention, legal holds and data loss prevention that all need to be understood.

How does this update change the way I govern private channels?

After the 20^th of September 2025:

• Retention policies that apply to ‘Teams channel messages’ will begin to apply to messages in private channels (that are associated with these policies).

• It will no longer be possible to apply retention policies to ‘Teams private channel messages’.

As this update will change the way existing retention is applied to your private channel messages, it is important that you assess your current policies and establish the ramifications of the update.

At a high-level there are four different scenarios that organisations might find themselves in: 

• If you haven’t yet created retention policies for your channel messages, then you won’t need to worry about this update. All it does is make it easier for you to apply retention to private channels in the future.

  
  

• If you have set up retention policies for your ‘Teams channel messages’ but haven’t yet configured retention policies for your ‘Teams private channel messages’, then this update will see the retention you have applied to your standard channels begin to apply to your private channels. I would imagine that for most organisations this will be a positive change, but anyone in this situation should consider the impact carefully.

  
  

• If you have set up retention policies for your ‘Teams private channel messages’ but haven’t yet configured retention policies for your ‘Teams channel messages’, then this update will mean that your private channel messages will no longer be subject to retention. I would expect that any existing messages that are being retained in your ‘substrate holds’ folder (i.e. which have been deleted but are being retained behind the scenes) will be automatically deleted once the update removes the private channel retention from them. Organisations in this situation will need to plan carefully to avoid loss of retained private channel messages.

  
  

• If you have applied retention policies to both your ‘Teams private channel messages’ and also to your ‘Teams channel messages’, then the way that your private channel messages are retained will switch from the former to the latter. This transition is only likely to result in issues if you have chosen to apply significantly different retention policies to the messages in the different types of channels. Organisations in this situation should evaluate their retention policies and consider how the update will affect their records.

  
  

While I’ve focused on the impact on retention here, there are some other potential ramifications that you might encounter:

• Data Loss Prevention

If you have any DLP policies that are applied to ‘Teams chat and channel messages’ and scoped to specific users, then these policies are likely to no longer apply to private channel messages (although they will still work for 1:1 chat messages).

To ensure that these DLP policies continue to apply to private channel messages after the 20^th of September, you will need to ensure that they are updated to include all Microsoft 365 Groups that have private channels. 

My guess is that very few organisations will have chosen to configure their DLP policies in a way that would be affected by this update, but it is worth checking precisely how your policies have been configured in Purview.

• eDiscovery and legal holds

Following this update, any eDiscovery holds that are configured to apply to a specific user’s Exchange mailbox will no longer apply to that user’s private channel messages. If you have an existing legal hold configured in this way, you will need to ensure that it is updated to include the Exchange mailbox of any relevant private channel’s Microsoft 365 Group.

Final thoughts

Private channels have always been one of the weird exceptions to the way retention works in Microsoft 365 that didn’t make a lot of sense.  It’s superb that we now have a way of applying retention to private channels contextually, so that different activities can be subject to their own appropriate retention.

I’m sure that some organisations will find challenges with managing the change introduced by this update - but I would imagine that only a very small number will actually face any real problems.

Certainly, once we are over the initial hurdle of the update itself, Microsoft’s retention options will be a little bit easier to understand and configure. Certainly, I know many organisations who will be absolutely delighted that they will finally be able to manage private channel messages more appropriately.

If you have any questions about this update or would like assistance with improving the way you govern information in Microsoft 365, please don’t hesitate to get in touch!