Outlook Unblock Attachment [patched] 〈2026 Edition〉

| Block Type | User Experience | Typical Cause | |------------|----------------|----------------| | | Attachment cannot be saved, opened, or even seen; user receives "Outlook blocked access to the following potentially unsafe attachments" | File extension in Level 1 list (e.g., .exe, .vbs, .js) | | Level 2 (Soft Block) | User can save to disk after a warning, but cannot open directly | File extension in Level 2 list (e.g., .reg, .cpl) | | Web / Tenant Block | "This attachment is blocked due to organization policy" | Microsoft 365 Safe Attachments or Exchange mail flow rules | Note: A fourth, silent block occurs when Outlook strips attachments entirely without notification—rare, but happens with malformed MIME or tenant anti-phishing policies. 4. Default Level 1 (Hard Blocked) File Extensions Outlook (and Exchange) block these extensions by default. This list is non-exhaustive but includes the most common:

Set-OrganizationConfig -BlockLevelOneFileExtensions $null # Disables all Level 1 blocks (DANGEROUS) Better: Remove specific extensions from Level 1: outlook unblock attachment

Cybersecurity & Messaging Team Document version: 2.0 Last reviewed: April 2026 End of Report | Block Type | User Experience | Typical