Modern eDiscovery workflows increasingly depend on links rather than traditional, static attachments. Nowhere is this more apparent than in Slack data exports. While Slack messages themselves are relatively straightforward to process, attachment URLs introduce a layer of technical and legal complexity that can quietly erode attachment coverage if not properly addressed.
This article explains how Slack attachment URLs work in exports, why access tokens and their status are critical, how those tokens can change after export, and why the order and manner in which you process Slack data can materially affect what attachments you ultimately see.
How Slack Attachment URLs Work in Exports
When Slack messages reference files—images, documents, videos, audio, or other uploaded content—the export does not always include the file itself. Instead, it frequently includes a URL that points to the attachment stored within Slack’s environment.
Access to that URL is governed by tokens. These tokens determine whether a given URL can be resolved to an actual file at the time you attempt retrieval.
At a high level:
- The message export contains the attachment URL.
- The URL requires a valid token to retrieve the file.
- The token’s validity depends on permissions, workspace membership, and timing.
From an eDiscovery perspective, the URL may look stable, but its ability to return a file is anything but guaranteed.
Token Status Is Not Static
A common—and risky—assumption is that attachment tokens captured at export time will remain valid indefinitely. In reality, token status can change after an export is generated, even while the underlying attachment remains fully intact and accessible within Slack.
Examples of token status changes include:
- Permission changes: A custodian or channel no longer has access to the file.
- Workspace or channel membership changes: The user associated with the token is removed or restricted.
- Export timing differences: A later export may generate a different token for the same attachment.
- Administrative actions: Security or retention policies affect token validity without deleting the file.
The result is a paradox that frequently surprises legal teams:
The attachment still exists and is actively used in Slack, but the exported link no longer resolves.
Export-Specific Tokens and the De-Duplication Trap
Slack tokens are export-specific, not globally persistent. This becomes especially problematic when you process multiple Slack exports across custodians, channels, or time periods.
Consider a common scenario:
- You process Export A first.
- Custodian A did not have access to certain attachments at export time.
- Tokens for those attachments are disabled or unresolved.
- You process Export B later.
- Custodian B does have access to those same attachments.
- New, valid tokens are generated for the same underlying files.
If your workflow is rigidly tied to the first token encountered, de-duplication logic may suppress later opportunities to retrieve the attachment. The system believes it has already “seen” the attachment URL, even though the original token was effectively dead.
In practical terms, the order in which Slack exports are processed can directly determine how many attachments you recover.
Why This Is a Broader Modern Data Problem
This challenge is not unique to Slack. It reflects a broader shift in modern data sources:
- Attachments are increasingly cloud-resident.
- Messages contain smart links, not files.
- Access is governed dynamically by permissions and tokens, not by static inclusion.
A smart link can go stale even while the referenced content is “living a happy life” in the source system—actively accessed, edited, and shared by users. Traditional eDiscovery tools, designed around static attachments, are often ill-equipped to handle this dynamic reality.
The Need for Token-Aware eDiscovery Workflows
To maximize attachment coverage, eDiscovery tools must avoid being permanently wed to the first token captured. Instead, they must support:
- Multiple tokens per attachment
- Cross-custodial token pooling
- Re-application of newly enabled tokens, individually or in bulk
- Re-attempted retrieval after initial failure
Without these capabilities, teams risk accepting initial attachment gaps as inevitable—when in fact they are often recoverable.
Real-World Impact: What Token Cycling Can Recover
In a recent StreemView matter, attachment URLs initially appeared incomplete when processed using standard workflows. However, by cycling through token lists across custodians and exports for each referenced attachment, StreemView was able to surface >100k additional attachments, amounting to >200 GBs in additional content.
Once retrieved, these attachments could be OCR’d, transcribed, and indexed, dramatically improving searchability and evidentiary coverage.
Had the workflow simply accepted the first-pass token results, these materials would have remained invisible—despite existing in Slack the entire time.
The Risk of Taking “What You Get” at Face Value
If you rely solely on what is initially available from a Slack export:
- You may have significant blind spots in attachment populations.
- Missing attachments may appear defensible, but are often technically recoverable.
- Review and search results may be skewed by incomplete underlying content.
In matters where attachments carry substantive meaning—contracts, images, spreadsheets, voice notes—these gaps can materially affect case strategy and outcomes.
Closing Thought
Slack attachment URLs are not broken, but they are dynamic. Tokens expire, permissions change, and exports reflect a moment in time—not the full reality of the Slack environment.
Modern eDiscovery requires tools and workflows that understand this distinction. The question is no longer whether an attachment exists, but whether your process is sophisticated enough to find it again when the first link fails.
For more examples of the complexities of working with Slack exports, see also our article on the hidden content that may be residing in the “Teams” folder in your Slack export.
