Previously, there was no functionality for exporting private messages but Slack today has added a new feature called “Compliance Exports” which allows administrators to export messages from private groups and direct messages, as well as edit history for messages in channels.
Compliance Exports will be disabled by default and requests must be made with a signed letter to Slack stating that the requester is allowed to access private information and that company policies allow for it.
When a request is made, all team owners will be notified and Slack staff will review the request manually. When Compliance Exports is turned on for the first time, team members will be notified that the feature is now active and that private messages could be exported.
Slack was careful to note that compliance exports are not retroactive, so if the feature is enabled today it won’t include past private chats, only those going forward.
➤ Slack’s Policy Update: What It Means to You [Slack blog]