Slack Retention Options and How They Affect Your Onna Syncs

Slack offers several message and file retention options that control how long your data is kept and whether edit and deletion history is preserved. The retention policy you choose directly affects what Onna is able to collect during a sync. This article explains each option and what to expect when Onna syncs your Slack data.

In this article:

• Overview

• Slack Retention Policies

• How Onna Syncs Behave Under Each Retention Policy

• Compatibility with Onna

Overview

Onna syncs Slack conversations at the conversation (channel) level. Your Slack retention settings determine whether Onna can capture message revision history and how deletions appear in your synced data. Understanding these settings helps you choose a policy that aligns with your preservation and compliance needs.

Note

Files shared in Slack are collected together with the channel they were shared in — they are not synced as standalone items. File-level retention is managed by a single organization-wide setting in Slack (see File retention below), and there is no option to override the org-level file retention policy for individual channels.

Slack Retention Policies

Slack lets an organization set retention policies for each type of conversation. The four message retention settings that affect your Onna syncs are described below, followed by the related override and file settings for reference.

Message Retention Settings

These options are available for public channels, private channels, and direct messages:

1. No organization-wide policy (public and private channels only)

   There is no governing organization policy, and individual workspaces set their own policies. Multi-workspace channels follow the org-level policy for their channel type. When no org-wide policy is in place, multi-workspace channels default to Keep all messages, but don't track revisions.

2. Keep all messages, but don't track revisions

   Slack keeps all messages in a workspace but does not retain a log of the original text before edits or deletions. Slack will still show that a message was edited or deleted.

3. Keep all messages, including revision history

   Slack keeps all messages, including logs of any edits and deletions and the user ID of who made the change, and includes them in an export.

4. Delete messages and their revisions after a specific number of days

   Slack checks daily for messages older than the number of days you select and permanently deletes them.

5. Delete messages and their revisions after a set number of days (full history still accessible via exports)

   Messages are deleted from the Slack UI after the retention period, but edit and deletion logs remain accessible through data exports or the Discovery API.

Retention overrides

1. No organization-wide policy

   Workspace Owners can modify override permissions at the workspace level.

2. Members – Always allow overrides

   Members can override retention for their private channels and DMs, and Workspace Owners can override it for public channels. This is always enabled and cannot be changed at the workspace level.

3. Members – Don't allow overrides

   Overrides are disabled and cannot be changed at the workspace level. If you choose this option, you can optionally enable Admin Overrides, which lets admins who manage channels set custom retention policies for individual channels (but not DMs).

Important

Channel overrides apply only to messages shared in a channel, not to files. Turning off member overrides (required to enable admin overrides) reverts any custom channel overrides back to the workspace- or org-level default for that conversation type. Depending on your policy, this may result in unintended data loss unless your policy is set to keep everything.

File Retention

1. Keep files

   Slack keeps all shared files. This does not include deleted files.

2. Keep files, but only for a specific number of days

   Slack permanently deletes all files (snippets, posts, uploaded files, and files shared via third-party apps like Google Drive, Box, or Dropbox) older than the number of days you select. Files shared via third-party apps remain stored in those apps, so deleting them in Slack does not affect the originals.

3. Keep all files, including deleted files

   Slack keeps all files for the lifetime of your workspace. Deleted files are available via exports and the Discovery API.

4. Keep all files, including deleted files, for a set number of days

   Slack permanently deletes files after the number of days you choose. Deleted files remain available via exports and the Discovery API for the retention period.

How Onna Syncs Behave Under Each Retention Policy

Keep all messages, but don't track revisions

Onna syncs the version of each message exactly as it appears in the channel at the time of collection. Because Slack does not track revisions under this setting, later edits are not captured.

Example:

• User A sends a message at 2:00 PM on 4/1

• Onna syncs the message at 2:30 PM on 4/1

• User A edits the message on 4/2

• Onna does not re-sync the message, because the sync already occurred before the edit

Keep all messages, including revision history

This is the best-case setting for capturing a message and all of its associated data. Edits and revisions appear on the date they occur, along with the latest version of the message.

Delete messages and their revisions after a specific number of days

This setting also captures a message and all of its associated data. Edits and revisions appear on the date they occur, along with the latest version of the message.

If you want deletions caused by Slack's retention policy to be reflected in Onna, you can enable Mirrored Syncing to mirror those deletions in Onna.

Note

Mirrored Syncing is available for Slack Enterprise Grid only and must be enabled for your account. Contact your CSM to enable this feature.

If data has been placed under a legal hold or preservation in Onna, it will be retained in Onna even if Slack deletes it at the source due to a retention policy. Legal hold takes precedence over retention-driven deletion.

Delete messages and their revisions after a set number of days (full history still accessible via exports)

Under this setting, every deletion caused by retention creates an entry in the data Onna collects. As a result, retention-driven deletions produce additional messages in your synced data. These entries are stored in Onna on the date of the deletion, not on the date the original message was sent.

Compatibility with Onna