Scute also allows you to use your card-based X.509 certificate to sign your emails with the S/MIME signature format. This has been tested with Mozilla Thunderbird only, but should work with any mail client with support for PKCS #11 (notably GNOME Evolution).
You must first load the Scute module into your mail client. With Mozilla Thunderbird, the procedure is the same as the one described above for Mozilla Firefox.
Then, open your account configuration dialog (
Settings), and in the
Security tab, under the section
Digital Signing, use the
Select... button to associate
your card-based certificate with your account.
When writing a new message, you may then use the
Digitally sign this message in the popup menu. You
will be prompted for your User PIN before the message is sent.