Turn off Protected View for attachments opened from Outlook
This user-scoped policy value determines whether Excel workbooks opened as Outlook attachments are opened in Protected View.
since 0.9.8.11
Purpose
Show registry keys (1)
HKCU\software\policies\microsoft\office\16.0\excel\security\protectedview\disableattachmentsinpv
This user-scoped policy value determines whether Excel workbooks opened as Outlook attachments are opened in Protected View.
When the REG_DWORD value disableattachmentsinpv is set to 1, Excel does not use Protected View for these attachments. A value of 0, or an unconfigured policy, causes the attachments to open in Protected View.
Protected View is a restricted, read-only mode for potentially untrusted files. It limits editing and restricts active content such as VBA macros and data connections.
Notes
Security
A value of 1 removes a layer of protection from Excel attachments opened from Outlook. The workbook is no longer initially opened in the isolated and functionally restricted Protected View environment. A malicious or manipulated attachment can therefore have more opportunity to interact with Excel and the system.
This setting does not automatically enable macros or other active content. Whether such content can run remains subject to other Excel and Office security policies, macro settings, the file type, and additional protection mechanisms.
Notes
This setting applies only to Excel files opened from Outlook. It does not change the equivalent Word or PowerPoint policies or other reasons for using Protected View, such as files from the Internet zone or potentially unsafe locations.
The 16.0 policy branch is shared by Office 2016, Microsoft 365 Apps, and later Office releases that use the same policy generation.
Microsoft documentation
Microsoft Learn: Microsoft 365 Apps security baseline settings – Protected View for Excel
Microsoft Support: What is Protected View?
Microsoft: Excel 16 administrative template (ADMX)