When an attachment remains blocked after attempting fixes:
Even if unblocked, attachments may be scanned by Safe Attachments (dynamic analysis). To allow a known safe file type:
April 14, 2026 Prepared For: IT Administrators, Security Teams, and End-Users Subject: Understanding, Managing, and Bypassing Outlook’s Attachment Security Filters outlook unblock attachment
For desktop users who frequently need specific blocked file types, you can permanently unblock them by editing the Windows Registry. This reduces security and should be done with caution.
OWA respects tenant-level policies. End-users cannot unblock Level 1 attachments in OWA unless the administrator has allowed them. Workaround: Forward the email to a non-Outlook email (e.g., Gmail) and download from there – but this creates a security gap. When an attachment remains blocked after attempting fixes:
| Action | Risk Level | Mitigation | |--------|------------|-------------| | Unblocking a single .exe from a known sender | Medium | Verify hash with sender via phone, scan with Microsoft Defender or VirusTotal | | Disabling Level 1 for .js organization-wide | Critical | Use only for a specific security group, and require signed scripts | | Using -BlockLevelOneFileExtensions $null | Severe | Equivalent to disabling inbound malware filtering; never do globally | | Renaming file extension to open | High | User may forget to rename back and double-click |
: Press Win + R , type regedit , and hit Enter. OWA respects tenant-level policies
: Changes will take effect after you close and reopen the application. 3. Corporate and Exchange Environments
Users who frequently receive legitimate blocked files (like .exe or .url ) and want to disable the filter for specific file types.