Remove file extensions blocked as Level 2
This string value (`REG_SZ`) identifies file name extensions that Outlook removes from the Level 2 attachment list.
since 0.9.8.11
Purpose
Show registry keys (1)
HKCU\software\policies\microsoft\office\16.0\outlook\security\fileextensionsremovelevel2
This string value (REG_SZ) identifies file name extensions that Outlook removes from the Level 2 attachment list. Multiple extensions are separated by semicolons within the value.
A Level 2 attachment cannot be opened directly from a message and must first be saved to disk. For an extension removed through this value, Outlook no longer enforces that restriction. Unless another security rule classifies the file type as Level 1, Outlook handles the attachment as an ordinary file type that is not classified as Level 1 or Level 2.
The value does not remove Level 1 restrictions or provide general access to blocked attachments.
Notes
Security
Removing an extension from Level 2 eliminates the required save-to-disk step before the attachment can be opened. Users can therefore open affected attachments more directly from a message. For file types capable of containing executable or otherwise active content, this reduces protection against accidental execution of malicious content.
The value does not disable separate Level 1 classification, security-software scanning, or server-side protection mechanisms.
Notes
The setting is effective only when Outlook Security Mode is configured to use Outlook Security Group Policy. It is a per-user policy for classic Outlook. Classic Outlook ADMX policies are not processed directly by new Outlook for Windows.
Microsoft documentation
Microsoft Learn: Information about e-mail security settings
Microsoft Support: Outlook blocked access to the following potentially unsafe attachments
Microsoft Learn: Map classic Outlook policies to new Outlook