I have a personal email signing certificate from Thawte. The certificate is issued in my name. The certificate is installed in the system.
If I look at the certificate from Internet Explorer Options/Content/Certificates, or from MMC, I see two purposes of the certificate: "proves your identity to a remote computer" and "Protects email messages".
But if I send an email signed with this certificate, and then look at the certificate already in the email (sent or received - same thing), I see only purpose "Protects email messages". Same in Outlook and in Outlook Express.
Why I don't see "proves your identity" purpose in the certificate in email?