Use UserIssuerSerialNumber

This policy setting determines whether Outlook uses IssuerSerialNumber as the SignerIdentifier, which enables third-party email client software applications to read encrypted Outlook email messages. For more information about Cryptographic Message Syntax, refer to the RFC 5652 specification.

If you enable or do not configure this policy setting, Outlook uses the IssuerSerialNumber as the SignerIdentifier.

If you disable this policy setting, Outlook uses SubjectKeyIdentifier for the SignerIdentifier, which might prevent third-party email client software applications from reading encrypted Outlook email messages.

Supported on: At least Windows 7
Registry HiveHKEY_CURRENT_USER
Registry Pathsoftware\policies\microsoft\office\16.0\outlook\security
Value Nameuseissuerserialnumber
Value TypeREG_DWORD
Enabled Value1
Disabled Value0

outlk16.admx

Administrative Templates (Computers)

Administrative Templates (Users)