Outlook: Forward as attachment emails in a PST file in new Outlook for Windows

🚨 The Signal: New Outlook for Windows now supports forwarding emails from PST files as attachments. This increases the risk of sensitive data exfiltration and complicates data governance and eDiscovery.

The Impact

All users are affected, increasing the risk of uncontrolled sensitive data sharing and complicating data governance.

• End users: Increased risk of inadvertently sharing sensitive historical data.
• Security teams: Harder to track and prevent exfiltration of legacy data.
• Compliance teams: Greater challenge in meeting eDiscovery and data retention obligations.
• Admins: New vector for data sprawl and potential data loss.

The Action

1. Review and update existing Data Loss Prevention (DLP) policies in Microsoft Purview to specifically address PST file content and sharing scenarios.
2. Communicate updated data handling guidelines to users regarding the sharing of information from PST files.
3. Implement or reinforce data retention policies for PST files to minimise the volume of legacy data.
4. Monitor Purview audit logs for unusual PST file activity or sharing events.

Impact: high · Workload: M365 Apps