Slack Retention Options and How They Affect Your Onna Syncs

Your Slack retention settings decide what Slack keeps, and Onna can only collect what Slack keeps. This article explains each Slack retention setting, what you will see in Onna under each one, and how Slack legal holds change that behavior.

In this article:

• Slack Retention Policies

• What Onna Collects Under Each Setting

• Slack Legal Holds

• Mirror Slack Enterprise Retention Settings

• Compatibility with Onna

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

If there is no organization-wide policy for public or private channels, each workspace sets its own policy. Multi-workspace channels then default to Keep all messages, but don't track revisions.

Note

Onna collects files with the message they were shared in, so in Onna, files follow the same retention behavior as their messages.

Retention overrides

Important

Turning off member overrides resets any custom channel overrides to the workspace or organization default for that conversation type. Unless that default keeps everything, this can cause data loss.

What Onna Collects Under Each Setting

The examples below use the same message: User A sends a message at 2:00 PM on 4/1, Onna syncs it at 2:30 PM on 4/1, and User A edits it on 4/2.

Keep all messages, but don't track revisions

• Collected: Each message as it appears at the time Onna syncs it.

• Edits: Not collected. In the example, Onna keeps the 4/1 version. The 4/2 edit is not captured because Slack does not keep a record of it.

• Deletions: If a message is deleted before Onna syncs it, Onna does not collect its content.

Keep all messages, including revision history

• Collected: Each message and its full edit and deletion history.

• Edits: Stored on the date they happen, with the earlier and later text. In the example, Onna has the 4/1 message and the 4/2 edit.

• Deletions: Stored on the date they happen, with the message content at the time of deletion.

Delete messages and their revisions after a specific number of days

• Collected: Messages and their edit and deletion history, as long as Onna syncs them before the retention period ends.

• Edits and deletions: Stored on the date they happen, as with the setting above.

• When retention ends: Slack deletes the message permanently, and it is no longer available to Onna. Anything Onna collected before then stays in Onna unless Mirror Slack Enterprise retention settings is turned on (see below).

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

• Before the set number of days passes: Onna collects each message and its full edit and deletion history, the same as Keep all messages, including revision history.

• After the set number of days passes: Slack removes the message from the Slack app and records the removal as a deletion. The message stays in the conversation as an empty placeholder, and its content moves into the deletion record.

• In Onna: Each removal appears as an additional deletion entry, stored on the date Slack removed the message, not the date it was sent. The entry contains the message content.

Expect your Onna data to include extra deletion entries that line up with your retention schedule. For example, with a 3-year policy, a message sent on 4/1/2023 appears on 4/1/2023, and a deletion entry with the same content appears on or around 4/1/2026.

Slack Legal Holds

Slack Enterprise Grid organizations can place legal holds on specific members. A hold keeps every message and file from the conversations those members belong to, even when a retention policy, an edit, or a deletion would otherwise remove them. A legal hold overrides any retention setting.

What happens when a held message reaches its retention date

Slack removes the message from the Slack app but keeps it, handling the removal the same way as the "full history still accessible via exports" setting above:

• The message stays in the conversation as an empty placeholder.

• The message content is kept in the deletion record, along with the original text and any earlier edits.

This happens for held content no matter which retention setting the workspace uses.

What you will see in Onna

• The original message, if Onna collected it before the retention date, stored on the date it was sent.

• A deletion entry containing the message content, stored on the date Slack removed it.

• Files from held messages that are later removed are collected in full and attached to the deletion entry.

If Onna syncs a held conversation for the first time after some of its messages have passed the retention date, those messages appear only as deletion entries, dated on the day Slack removed them.

Limits of Slack legal holds

• If a channel is deleted, its messages and files are not kept, even under a hold.

• Slack does not include Slack Connect conversations, emoji reactions, or snippet version history in legal holds.

Mirror Slack Enterprise Retention Settings

Mirror Slack Enterprise retention settings is an optional account setting. When it is turned on, Onna removes its copy of a message once the message passes the channel's Slack retention period, so Onna matches Slack. Data under an Onna preservation is never removed. A Slack legal hold does not stop this removal, because it only keeps data in Slack.

Compatibility with Onna