Outlook: S/MIME support for Shared Mailboxes and Delegate Mailboxes in New Outlook for Windows

🚨 The Signal: New Outlook for Windows now supports S/MIME for shared and delegate mailboxes. This enhances email confidentiality and integrity for collaborative accounts, reducing data exposure risks for sensitive communications.

The Impact

Users of shared and delegate mailboxes are affected, with a positive security risk reduction due to enhanced email protection.

• Shared mailbox users: Reduced risk of email interception and tampering.
• Delegate mailbox users: Improved confidentiality for sensitive communications.
• Security teams: Enhanced compliance with data protection policies.
• Organisations: Stronger email security posture for collaborative work.

The Action

1. Ensure S/MIME certificates are properly deployed and managed for all relevant users and mailboxes.
2. Communicate S/MIME capabilities and best practices to users of shared and delegate mailboxes.
3. Review existing email security policies to incorporate S/MIME usage for shared/delegate scenarios.
4. Monitor S/MIME usage and certificate validity through Microsoft Purview or other security tools.

Domain: Exchange · Impact: medium · Workload: Exchange Online