Slack: Prevent Files Being Uploaded To a Conversation With People From Another Company?

Sharing files externally in Slack can be very convenient for collaboration. However, it also introduces security risks that organizations need to consider. When external users upload files, there is a chance that sensitive information could be accidentally exposed or accessed by unauthorized individuals. That is why it is important to understand these risks and implement safeguards.

External file sharing means allowing users outside your organization, such as clients, partners, or contractors, to upload or view files within your Slack workspace. While this facilitates fast communication, it can also open doors for data leaks, malware, or accidental sharing of confidential data.

Potential Security Risks of External File Sharing

Data leakage: External uploads might include confidential documents or personal information that should not be shared outside your company.
Malware and viruses: Files from external sources can contain malicious software. Opening these files may compromise your system security.
Unauthorized access: If permissions are not carefully managed, external users might access more data than intended, leading to security breaches.
Loss of control: Once a file is uploaded to Slack, it can be downloaded, forwarded, or stored elsewhere. This makes it harder to monitor or revoke access.

Why Organizations Need to Monitor External File Uploads

Monitoring and controlling external file uploads help organizations protect sensitive information and reduce security threats. Without proper oversight, files containing sensitive data might be shared unintentionally. Keeping track of what is uploaded and by whom allows quick action if something suspicious occurs.

Implementing policies and using Slack’s security features can prevent accidental leaks. For example, setting restrictions on who can upload files externally reduces the risk. Regular audits of shared files can also identify potential vulnerabilities early.

Best Practices to Manage External File Sharing Risks

Set permissions carefully: Limit who can upload or share files with external users. Use Slack’s admin controls to restrict external access where possible.
Use secure channels: Encourage sharing sensitive files only in secure, private channels with controlled access.
Enable file review processes: Regularly review shared files for any sensitive or inappropriate content.
Educate your team: Train staff on the importance of data security and the risks of sharing files externally.
Implement malware scanning: Use third-party tools or Slack integrations to scan uploaded files for viruses before they are accessed.

Understanding the risks involved with external file sharing in Slack is crucial for maintaining data security. By applying the right controls, monitoring uploads, and educating users, organizations can enjoy the benefits of collaboration without compromising their sensitive information.

How to Set Permissions for External Users

Managing permissions for external users in Slack is essential to keep your workspace secure and control what outside collaborators can access. External users, such as guests or partners, should have limited access to prevent unauthorized file uploads or sensitive information exposure. This guide walks you through the steps to configure these permissions effectively.

Access Slack Admin Settings
Log in with your admin account. Click on your workspace name at the top left corner, then select Settings & Administration > Workspace Settings. From there, go to the Permissions tab.
Navigate to Guest and External User Settings
Within Permissions, find the section labeled Guest Users & External Access. Here, you can manage what external users can do and see. Look for options related to file uploads and sharing.
Configure Guest User Roles
Choose the type of guest account—single-channel or multi-channel. For better control, assign guests to a specific channel only. This limits their access to the rest of your workspace and reduces risks of unauthorized uploads.
Restrict File Uploads for External Users
Find the setting labeled Allow External Users to Upload Files. Turn this option off if you want to prevent external users from uploading files. If you need external users to share files within their assigned channels, enable only that specific permission.
Adjust External Access Settings
Navigate to External Access options. Here, you can allow or disallow external emails and domains. Limiting this helps prevent unauthorized external users from joining or uploading files without approval.
Save Changes and Review Permissions
After adjusting settings, click Save. It’s good practice to review your workspace permissions regularly. Make sure external user restrictions align with your organization’s security policies.

It is helpful to test permissions by adding a test external account. Verify that the user cannot upload files if restrictions are in place. This way, you avoid surprises when actual outside users access your workspace.

Keep in mind that Slack updates its permission features periodically. Check the latest documentation or support resources if options appear differently or if you encounter issues. Proper permission management helps protect your sensitive information while allowing productive collaboration with external partners.

Restricting File Uploads in Slack Channels

Restricting file uploads in Slack channels is an effective way to enforce organization-wide file sharing policies and prevent inappropriate or unnecessary files from being shared. This feature can help maintain a cleaner workspace and reduce clutter. While Slack does not allow channel-specific file upload restrictions directly from the user interface, there are ways to control and limit file sharing using admin settings and policies.

If you are a workspace owner or admin, you can manage file sharing permissions to better control what is uploaded and where. This helps ensure sensitive information stays within designated channels or is properly managed. Here are the methods you can use to restrict file uploads in Slack channels:

Adjust Global File Upload Settings

Slack allows workspace administrators to control file sharing at the overall level through admin settings. To do this:

Open your Slack workspace and click on your workspace name at the top left.
Select Settings & Administration, then choose Workspace Settings.
Navigate to the Permissions tab and look for File Sharing.
Here, you can choose to disable file uploads for all members or allow only certain files, like images or PDFs.

This setting blocks or limits file uploads across all channels, but for more granular control, consider other methods.

Use User and Admin Policies to Limit Sharing

Slack allows admins to set policies that restrict who can upload files or share in specific contexts:

Go to Slack App Directory.
Select Policies & Management to create or modify sharing policies.
Define roles and permissions to restrict file sharing to certain users or groups.

For example, you can restrict file uploads to only workspace owners or admin users, thereby preventing regular members from sharing files in sensitive channels.

Implement Channel-Specific Guidelines through Naming Conventions and Admin Monitoring

While Slack does not offer direct per-channel upload restrictions, you can implement guidelines and monitor activity:

Name channels clearly to indicate sharing policies, such as #no-files or #confidential.
Regularly review channel activity through audit logs available in Slack Enterprise Grid or via third-party tools.
Set expectations with your team about what can and cannot be shared in each channel.

If necessary, communicate that file sharing is only allowed in designated channels, reinforcing organization policies.

By combining these settings and best practices, you can effectively limit or restrict file uploads in Slack channels. This helps maintain compliance and keeps your workspace organized without sacrificing essential collaboration features.

Best Practices for Managing Cross-Company File Sharing

Sharing files securely across different organizations can be challenging but is essential for smooth collaboration. To prevent data leaks and protect sensitive information, it is important to follow best practices for cross-company file sharing. These strategies help ensure that your data is shared safely while maintaining efficient workflows.

Establish Clear Policies and Permissions. Create formal guidelines on who can share and access files. Define user roles and permissions based on job responsibilities. Regularly review access rights to ensure only authorized personnel can view or modify sensitive data.
Use Secure File Sharing Platforms. Choose trusted cloud services or enterprise file sharing tools that offer encryption, access controls, and activity logs. Examples include Dropbox Business, Google Drive with advanced security features, or specialized solutions like SharePoint.
Encrypt Sensitive Files. Before sharing, encrypt important documents. Encryption converts files into a format that requires a password or key to access. This adds an extra layer of security, especially when sharing via email or unsecured networks.
Implement Two-Factor Authentication (2FA). Enable 2FA on sharing accounts to prevent unauthorized access. Even if login credentials are compromised, 2FA provides an additional security step.
Share Links with Care. When generating share links, set expiration dates and restrict permissions (view-only or edit). Avoid sharing links publicly or via insecure channels. Always verify recipients before sharing confidential files.
Regularly Monitor and Audit Access. Use activity logs to track who accessed, downloaded, or modified files. Regular audits help identify suspicious activity early, allowing prompt action to prevent data leaks.
Educate Employees on Security Best Practices. Conduct training sessions on secure sharing protocols. Teach staff to recognize phishing attempts, avoid sharing passwords, and report security concerns.
Establish Data Retention and Disposal Policies. Define how long shared files should be kept. Securely delete documents when they are no longer needed to reduce risk exposure.

For example, a company working with multiple clients might establish a third-party portal with restricted access to project files. They set expiration dates for each link and require two-factor authentication. Regular audits ensure that only current project members can access the data.

Common mistakes to avoid include sharing passwords via insecure channels, neglecting access reviews, and using weak encryption methods. Following these best practices helps protect customer data, intellectual property, and other sensitive information when sharing files across organizations.

Configuring Slack for Better Security with External Teams

When working with external teams on Slack, security is a top concern. Properly configuring your Slack workspace can help protect sensitive information while still promoting effective collaboration. This guide walks you through key settings and best practices to enhance security without limiting productivity.

Review and Manage Guest Accounts

Slack allows you to add different types of guests, like Single-Channel and Multi-Channel guests. To prevent unauthorized access, regularly review guest accounts and remove those who no longer need access. Navigate to your workspace settings by clicking on your workspace name, then select Administration > Manage members. Here, you can see all users, including guests. Keep track of their permissions and restrict access to only necessary channels.

Set Up External Access Controls

Slack provides options to control how external users interact with your workspace. Under Settings & Permissions, look for External sharing. Disable or limit guest invitations to prevent external users from inviting others or creating new channels. You can also restrict file sharing with external users to protect sensitive data.

Enable Two-Factor Authentication (2FA)

Adding 2FA adds an extra layer of security. Encourage all members, especially external collaborators, to enable 2FA on their accounts. This reduces the risk of unauthorized access if login credentials are compromised. Users can activate 2FA in their account settings under Additional Security.

Limit Permissions with User Groups and Channel Settings

Use Slack’s user groups and channel-specific permissions to control who can post or view sensitive content. For example, create private channels for confidential discussions and restrict access to internal teams only. Regularly review channel memberships to ensure they align with current project needs.

Implement Security Alerts and Monitoring

Slack’s Enterprise Grid offers monitoring tools that alert administrators about unusual activities, such as failed login attempts or abnormal file sharing. Enable these features if available, or use third-party integrations for added oversight. Regularly checking activity logs helps detect potential security issues early.

Promote Security Awareness Among Users

Educate your team and external collaborators about best security practices. Encourage strong, unique passwords and caution against clicking suspicious links. Remind everyone to log out from shared devices and avoid sharing login credentials.

By carefully adjusting these Slack settings, you can significantly enhance the security of your workspace when working with external teams. It strikes a balance between keeping your data safe and maintaining open, efficient communication with collaborators.

Step-by-Step Guide to Limit External File Uploads

If you want to control your Slack workspace and prevent members from uploading external files, this guide will walk you through how to limit or disable external file uploads. This can improve security, reduce clutter, and maintain company policies. Follow these steps to adjust your Slack settings effectively.

Access Slack Workspace Settings: Log in to your Slack account with administrative privileges. On the desktop or web app, click on your workspace name at the top left corner. From the dropdown menu, select Settings & administration and then click Workspace settings. This opens your workspace’s admin panel.
Navigate to Permissions: In the workspace settings page, look for the tab labeled Permissions or Settings. Click on it. Depending on your Slack plan, some options may vary, but you’re aiming for file and message sharing permissions.
Find External File Upload Settings: Scroll through the permissions page until you locate the section titled File sharing or External file uploads. Here, you will see options related to who can upload files from outside sources.
Adjust External Upload Restrictions: You will typically see options like:
- Allow uploads from external sources: Enable or disable this setting.
- Limit to certain channels: Restrict external uploads only to selected channels.
To completely prevent external file uploads, toggle the setting to off. If you want to restrict uploads to specific channels, select those accordingly.
Save Changes: After adjusting the settings, scroll down and click the Save button. Changes take effect immediately or after a brief refresh.
Communicate Changes to Your Team: Inform team members about the new file upload policies. Clear communication helps prevent confusion and ensures everyone complies.

In some cases, Slack workspace administrators might not see these options due to plan limitations or user permissions. If you cannot find the external upload restrictions, check your plan compatibility or contact Slack support for help. Additionally, for organizations seeking advanced control, consider integrating third-party tools or setting up policies through your company’s IT department.

Keep in mind that restricting external file uploads can help prevent accidental data leaks and maintain a cleaner workspace. Always review your settings periodically to ensure they match your team’s needs and security standards.

Troubleshooting Common External File Upload Issues

Experiencing difficulties when uploading external files to Slack is a common problem for many users. These issues can stem from various causes, such as file size limits, internet connectivity, or permissions. Fortunately, most problems can be resolved quickly with a few troubleshooting steps. This guide will walk you through the most common external file upload issues and how to fix them effectively.

Check File Size and Format
Slack has restrictions on file size and types. Typically, files up to 1GB can be uploaded, but this may vary depending on your workspace plan. Also, certain file types might be blocked for security reasons or policy settings. To troubleshoot:
- Ensure your file does not exceed Slack’s maximum size limit.
- Confirm the file type is supported. Commonly allowed formats include images, documents, and PDFs.
- If the file is too large, consider compressing it or splitting it into smaller parts before uploading.
Verify Internet Connection
A stable internet connection is crucial for uploading external files. Interrupted or slow connections can cause upload failures. To troubleshoot:
- Test your internet speed using an online tool to determine if your connection is stable.
- If your connection is slow or dropping, try resetting your router or switching to a different network.
- Ensure no other bandwidth-heavy applications are running during your upload.
Check Permissions and Settings
Your workspace or team admin may have set policies that restrict external file uploads. Also, individual user permissions might limit file sharing features. To troubleshoot:
- Confirm that you have permission to upload external files in your Slack workspace.
- If you are unsure, contact your Slack administrator to verify if external uploads are allowed.
- Review your Slack app permissions in your user settings to ensure file sharing is enabled.
Clear Cache and Refresh
Sometimes, browser or app cache issues hinder file uploads. Clearing cache can resolve temporary issues. To troubleshoot:
- If using Slack on a browser, clear your cache and cookies, then restart the browser.
- If using the Slack desktop app, try restarting the app or reinstalling if necessary.
- Log out and log back in to refresh your session.
Update Slack App or Browser
Outdated apps or browsers can encounter bugs affecting file uploads. To troubleshoot:
- Check for the latest version of the Slack app and update if needed.
- If using a browser, update to the newest version or try a different browser.
- Restart your device after updates for best results.

Troubleshooting Step	Possible Cause	Solution
File too large or unsupported type	Exceeds size limit or blocked format	Compress or change the file type; check Slack limits
Unstable internet connection	Network issues causing upload failure	Improve connection, reset router, reduce bandwidth usage
Permission restrictions	Admin policies blocking external uploads	Contact admin, verify permissions, or adjust settings
Browser or app cache issues	Corrupted cache preventing upload	Clear cache, restart app/browser, log out and in again
Outdated software	Older app or browser versions	Update Slack app or browser to latest version

By following these troubleshooting steps, most common external file upload issues in Slack can be resolved quickly. Always start by checking file size and permissions, then verify your network and software updates. If problems persist, reaching out to your Slack administrator or support team can provide additional assistance.