User Configuration > Administrative Templates > Microsoft Outlook 2016 > Security > Cryptography > Signature Status dialog box
User
HKCU\software\policies\microsoft\office\16.0\outlook\security
This policy setting allows you to treat Level 2 errors as warnings instead of errors. Level 2 errors occur when the message signature appears to be valid, but there are other issues with the signature. If you enable this policy setting, Level 2 errors will be treated as warnings. If you disable or do not configure this policy setting, Level 2 errors will be treated as errors When you specify a value for PromoteErrorsAsWarnings, note that potential Level 2 error conditions include the following: - Unknown Signature Algorithm - No Signing Certification Found - Bad Attribute Sets - No Issuer Certificate found - No CRL Found - Out-of-date CRL - Root Trust Problem - Out-of-date CTL